Basically the four main plot points are:

(that I wanted to do four threads on in the forum and keep them going so as to hone in on the pony version.)

1. Fëanor Arc -- Since the readthrough didn't happen -- spoilers ahoy.

Points of Adaptation in this section:

Valinor = Alinor (where the alicorns lived)
The Noldor = Alicorns (for the most part)
Two Trees of Valinor = Two Trees of Harmony
Prince Fëanor of the Noldor = Princess Starfall (corresponds to Fire Spirit, the ponified / male version of the character)
Melkor / Morgoth = Tirek
Ungoliant, mother of spiders = Unpleasant the spider, mother of Changelings
Angband = Tartarus; Balrogs = Balgriffs (fiery, ancestral relatives of griffin race)
Yavanna = Shyavanna, goddess of nature
Galadriel = Luna and Celestia (character expansion)
"gods and goddesses" = simplification for synopsis. they are "angelic" beings
Fingolfin, half brother of Fëanor = the Mother of Celestia (half sister of Luna)
Other elves who proceeded with Fingolfin = Pegasi (crossed over with Vanyar)
Grey Elves = Unicorns; Men (not born yet) = Earth Ponies
Sea-Elves = Sea-Ponies
Silmarils = The Elements of Harmony ("original edition")
Beleriand = Alfalfaland (similar geography, see map)

1. Fëanor Arc -- The elves awake in the deeps of time, before any other sentient beings exist. The Gods, fearing the wrath of God of Evil Melkor who lives in the far North of Middle-Earth, invite the elves to live in Paradise across the western sea for their own protection. This is the origin of elves having more magical power than humans. Fëanor, the greatest and most skilled of all the Elves, is born in Valinor (Paradise aka the Undying Lands in the west). He is extremely prideful and vindictive but talented. He discovers how to capture the light of the Two Trees of Valinor, which light the world at the time, in the form of three holy jewels, the Silmarils. But Morgoth, aka Melkor, tricked the Elves. He incites envy and jealousy between them and convinces Feanor to hide the Silmarils away. The Gods call for a great feast on Mount Taniquetil (sort of Tolkien's version of Asgard) to try and mend feelings between Feanor and his younger brother (by a different mother), Fingolfin, who is the most valiant of the Elves. During the feast, Melkor sneaks into Valinor with Ungoliant, the mother of all spiders, a Cthulu-esque being, and together they poison and kill the Two Trees and steal the Silmarils from the vault of Feanor's fortress. Finding this out, Feanor is filled with rage and incites the Elves to rebel against the Gods, leaving Valinor for Middle Earth to wage war on Morgoth without their blessing. The greatest orator of the elves, he makes an infamous speech, the Oath of Feanor, calling on the elves to swear undying vengeance to the end of the world (elves are immortal, remember) on anyone who would have, or hold, a Silmaril except for Feanor and his folk. (His seven sons swore the oath with them). This is the Elvish "fall from grace" when they were "cast out of paradise" because during the Flight of the Noldor (high elves, Feanor's people) they killed the Sea-Elves and stole their swan-ships in order to make the crossing to Middle-Earth. Because of a previous commitment, Fingolfin feels bound to follow and all his people, but they are betrayed in the icy wastes of the Grinding Ice, when Feanor decides to burn the ships and commit his forces to attack Morgoth prematurely in his fortress of Angband (essentially Tartarus or Hell), leaving Fingolfin's forces stranded on the shoreline. The Gods curse them for their role in the Kinslaying of the Sea-Elves on the shores of Paradise, so they feel compelled to move forward, crossing the Grinding Ice on foot. Meanwhile, Feanor and his elves, fresh from the Undying Lands, wipe out Morgoth's army of orcs who have been harassing the native Grey-Elves (wood elves, who stayed behind and did not make the crossing to Valinor) in the enchanted forests of Beleriand. Pressing ahead and full of righteous rage, Feanor fights multiple Balrogs alone within sight of the Gates of Angband (Tartarus / Hell) and is fatally wounded. He curses Morgoth with his last breath, pledging to have a role in defeating Morgoth at the end of days, then his body burns away. Now, the reason Feanor was angry at the Gods was that when the Two Trees died, their creator Yavanna, goddess of nature, said that she could not recreate them; only the light from the Silmarils could revive them (sound familiar?) and doing so would break the Silmarils. Feanor refused to give them up, saying he also could not create them again; then they discovered the Silmarils had been stolen by Morgoth from where Feanor hid them away. So after the Elves left, Yavanna and Varda (goddess of the stars and light) took the last two fruits of the two trees and turned them into the sun and moon, which they set in the sky for the first time, right as Fingolfin and his host made it across the Grinding Ice to Middle Earth. Blinded by the light of the sun and moon, the forces of evil were driven back, Feanor's sons were saved, but his eldest son was taken captive and chained to the cliffs of Thangorodrim, the volcanic peaks above Angband (Tartarus). Fingolfin became the High King of the Elves in Middle Earth, and they settled among the grey-elves in the enchanted kingdoms of Beleriand. Galadriel, Feanor's cousin, went to live in the forest of Doriath with Thingol, the ancient elf-king of Beleriand, who lived in the caves there; but discovering what had happened in Valinor, Thingol banished the Noldor (high elves, Fingolfin and Feanor and Galadriel) from Beleriand and banned their language, but the Noldor were more powerful and they settled voluntarily in the mountains to the north, facing the fortress of Angband whose doors were sealed shut. In an important act, Fingolfin's son rescued Maedhros, Feanor's son, from imprisonment where he was chained to a cliff, cutting off his hand in the process but reuniting the two families in peace. And thus began the long peace of Beleriand, when the doors of Angband were shut and Elves ruled Middle-Earth.

So yeah, that's the first of four story arcs. The idea is to make this an ongoing thread for story adaptation discussion.

I posted it in this thread, in hopes that people think it's worth commenting on how it relates to the pony version?

I'd love to discuss the adaptation with... people in general.

Part 1 -- Fëanor Arc (this part)
Part 2 -- Tale of Beren and Lúthien -- story adaptation thread
Part 3 -- Tale of Túrin (of Pinkamena and the Children of Píe)
Part 4 -- Tale of Gondolin (of the Voyage of Clover the Clever)

My first thoughts:

Tirek -- both G4 and G1 -- is a really, really good fit with Morgoth; but I think there are some other parallels that could be made here. As a list, for convenience and because I apparently really like walls of text:

* Manwe and Mandos have an enormous amount in common with Princesses Celestia and Luna respectively. Celestia and Manwe both seem to have problems thinking like other people, are both forgiving, and are both pretty cagey and cautious. Luna -- especially the mature, confident Luna of seasons 3 and 4 -- is darker and gloomier than her sister, and is definitely a prophet of doom a few times. I'd recommend casting the sisters as these two -- whatever "casting" may mean -- and filling up the rest of the Valar as needed.

(Now that I think of it, Discord as Tulkas would be hilarous, and yet that casting would work.)

* Celestia as Manwe also helps me to better understand, and make peace with, Manwe's apparent uselessness. He was so hesitant to act because every time he acted, he reshaped the geography of the world, and not in the good way. Magic in Tolkien's world affects the area around it, if it's powerful enough, and the powers Valar use to fight each other are definitely powerful enough. The war in the Elves' period destroyed half of the north, and left clouds of dust darkening the northern sky for centuries; the War of Wrath sank Beleriand; the destruction of Numenor, which admittedly wasn't Manwe's action but was definitely due to his request to Illuvatar, drowned a lot of the wastern coastline of Middle-earth. If Princess Celestia's horn shot atomic bombs instead of beams of magic, she'd be pretty reluctant to attack her enemies, too!

* Queen Chrysalis would make a disconcertingly good Ungoliant -- partially inspired by your association of Ungoliant with Changelings, but I could definitely see Tirek and Chrysalis partnering and having a Morgoth-and-Ungoliant-type falling out.

* I compared Sunset Shimmer to Feanor on another thread. She's more moral than Feanor was, but also more prone to going off half-cocked. Her will is very strong in some respects (she can handle a sledgehammer like a baseball bat, and strength like that doesn't happen by accident), but very weak in others; she's guileless, she doesn't plan ahead, and in heated moments she's ruled by her emotions. Tirek, who even managed to manipulate Discord, could play her like a flute; swearing an unbreakable oath, frightening the Teleri into giving up their ships, slamming a door in Tirek's face (wait, Finwe did that one), drawing a sword on her half-sister, and giving Luna/Mandos the middle finger as she sails off to new adventures are all very Sunset Shimmer things to do. I may have to write that myself, if you don't mind.

* Fluttershy would make a really good Yavanna but also a really good Luthien. Yavanna doesn't have much of a role in the story, though, so I'd advise keeping Fluttershy as Luthien.

* I'd recommend making Angband Midnight Castle and Valinor Canterlot, but I really like Tirek ruling the griffins (who'd play the role of both orcs and balrogs -- fittingly enough, meaning more personal combat and less army-scale battles. Who knows how much of Season 5 the Ponymarillion is going to call?). The geography even matches, with the environs of Angband being east of Canterlot, requiring that you either have boats or walk across an icecap to get there!

* Bonus points, you could have Dream Valley be Beleriand -- or maybe Dream Valley as Hithlum within a larger West Griffonstan as Beleriand. (So evidently the ponies migrated west... did Tirek kill a few windigoes to acquire his kingdom, I wonder? Or, better: did he enslave them? Could the Windigoes be dragons?! I could definitely see an elemental being of ice and hatred having Glaurung's personality.)

* Perhaps Ulmo could be played by the King of the Seaponies, and his favor could be represented by actual seapony armies rather than by latent powers in water...

* I'd also recommend making the three elven tribes the three pony tribes: unicorns as Vanyar, pegasi (the most intrepid and militaristic of the three tribes) as Noldor, earth ponies as Teleri and Umanyar. If Sunset does slaughter the Earth Ponies at their havens -- or just frightens them, drives them off, and siezes their ships, since she had few compunctions about intimidation and robbery in her pre-reformed period -- then her followers finding themselves in an Earth Pony kingdom would definitely underline how uncomfortable this was.

* Galadriel... I know I was thinking of a pony who could plausibly be Galadriel to Sunset's Feanor, but I can't remember who I was thinking of. Maybe I had Rarity or even Twilight in mind...

* For the other Noldorin leaders, I'd vote to mostly use pegasi. I saw one story where Sunset Shimmer was Spitfire's sister; if Sunset Shimmer is accusing Spitfire of snivelling cowardice, Feanor's confrontation of Fingolfin (4th item on this page) shines through in all its egregiousness.

* Sunset's seven daughters might or might not end up being OCs. Maedhros was awesome, Maglor memorable, Celegorm nasty and incompetent to the point of almost being comic relief (I strongly recommend Limyaael's "The Game of the Gods", by the way). The rest are sort of a blur, but still. (Perhaps Sunset married a very overwhelmed Flash Sentry.)

* I'm not really sure how humans can be made to fit into the story... but, come to think of it, if absolutely all else fails, this fandom is notorious for its Human in Equestria fics, many of which involve Fluttershy. However, this would very rapidly decay into self-parody...

* Absolutely no idea what to do with the dwarves, though.