Here's a possible alternate universe idea for this series (and, yes, I AM fully aware of the irony of suggesting an alternate universe idea FOR a series that's ALREADY an alternate universe, so don't bother pointing that out):

What if ALL the Hero Souls came from the SAME alternate universe:

For example:

DC Universe:

Twilight Sparkle: Billy Batson/Captain Marvel (or Shazam if you prefer to use THAT name) - Strength, speed and flight at least on a par with Superman as well as marginally more invulnerable than Superman (owing to having no real physical weaknesses in super-form PLUS a higher resistance to magic attacks). Plus, Billy (at least pre-new 52) is EVEN MORE of an overgrown boy scout than Superman is classically, so he would still make an excellent Soul of Hope

Shining Armor: Green Lantern (either Hal Jordan or John Stewart, depending on the author's preference) - to be fair, his talent with force fields is a pretty good indication that he could learn to mimic the abilities of a Green Lantern power ring with enough practice.

Big Mac: Kal-El/Clark Kent/Superman - Raised by farmers, nice guy and is already one of the strongest mortal ponies in Equestria.

Applejack: Princess Diana of the Amazons/Diana Prince/Wonder Woman - (usual) emphasis on honesty, uses a rope more of than most of the other canon ponies, pretty strong for a mortal pony.

Rainbow Dash: Wally West/the Flash (well, Rainbow IS closer to Wally in personality than she is to Barry) - I mean, well, duh!

Pinkie Pie: Jon`n Jon`zz/Detective John Jones/too many other aliases to list here/Martian Manhunter - Well, to be fair, her having powerful telepathy would be a good way to explain how she knows so much about so many, being able to change her shape into that of extremely small animals as well as turn intangible would be a good way to explain how she can fit through ridiculously small openings with ease and super-strength, super-speed, flight and super-durability would cover most of the other seemingly impossible things Pinkie makes look so easy.

Rarity: Bruce Wayne/Batman - Previous episodes have shown her demonstrating surprising skill in both martial arts AND detective work, all of her fashion work would be great for developing disguises AND she has more upper class leanings than the rest of the Mane Six.

Fluttershy: Orin/Arthur Curry/Aquaman - Might be interesting to see Fluttershy's natural knack with animals upgraded to a flat-out telepathic link. Plus, her being strong and durable enough to withstand ocean bottom pressures would be a big help in dealing with particularly stubborn and powerful animals. In addition, her having senses specially adapted for deep water living (perfect night vision being just ONE of them) could come in surprisingly often.

Spike: Dick Grayson/Robin I/Nightwing - Well, I couldn't think of anybody better. Still, Spike COULD benefit from having Dick's acrobatic experience and the assorted skills Dick learned from Bruce on top of his canon dragon abilities and the stuff he learned from Twilight. In addition, both Dick and Spike are smart-alecs, but while loyal to their friends, also unafraid to speak their minds.

******************************************

If we were going for all-Marvel:

Shining Armor: Steve Rogers/Captain America (minus the garbage the comics have been pulling with him lately) - nice guy most of the time, trained solider, built-in shield, YOU do the math.

Twilight: Reed Richards/Mister Fantastic - both among the smartest characters in their respective universes, both tend to focus too much on intellectual pursuits and yet, both are also generally quite firmly on the side of good most of the time and both are also pretty loyal to their friends.

Pinkie Pie: Peter Parker/Spider-Man - Oh, come on, you probably saw THIS coming a mile away.

Fluttershy: Bruce Banner/the Hulk - both are generally meek and shy, but both also have powerful monsters of pure rage inside (in Fluttershy's case, it's [usually] more figurative than literal, but the fact still remains)

Spike: Ben Grimm/the Thing - both are among the most loyal friends of Reed/Twilight, not to mention Spike DOES have the potential to gain the strength and durability that Ben has as the Thing.

And, that's all I can think of for the Marvel end.

***************

Unfortunately, I don't have the time and energy to tackle this AU idea myself, but anybody who wants to share their visions of a "Reincarnationverse" where ALL the Hero Souls came from the SAME universe is perfectly welcome to share their views. You can use DC, Marvel (and not even necessarily the same characters I did) or even another universe entirely.

5921487 I will wholeheartedly endorse this for whoever decides to give it a go.

5921565 Thanks very much, Sven. :-D

The only change I would recommend would be having Twilight be Hank McCoy. Reed has a caber shoved so far up where the sun doesn't shine it isn't funny. With Rainbow Dash being Johnny Storm to play off Spike.

5922056 Well, that's fair enough, bn. As I think I said earlier, if the author respectfully disagrees with the casting examples, they can change it however they choose.

And I think I ALSO have a good idea of why all the Hero Souls would be from the same universe: the VILLAIN Souls are ALSO all from the same universe, so the powers that be need the souls of those who know how to fight said Villain Souls:

For example:

All DC:

The Joker (author's choice who gets the soul of course; same for all the other examples)

Lex Luthor

The Reverse Flash (author's choice which incarnation)

Ra`s al Ghul

Brainiac

General Zod

Black Adam

Sinestro

Darkseid

Plus any other major DC villains the author can think of

*************

All-Marvel

Red Skull

Magneto

Doctor Doom

Norman Osborn/Green Goblin

Loki

the Super-Skrull

Ultron

Thanos

Plus any other major Marvel villain the author can think of

************

Again, these are just examples. Anybody who likes the idea enough to use it is perfectly free to use their own casting ideas, or even pick a different universe for the souls to come from entirely