The Mane 6 are destined to bear the Elements · 3:40am Feb 24th, 2018
A popular topic of fan speculation is alternate Element Bearers – whether they would be entirely different characters, or with Sunset Shimmer instead of Twilight, or with the Mane Six as the Bearers of different Elements than in canon. While it's fun to imagine, my view is that this premise is not a mere example of the butterfly effect. Instead, these scenarios belong in an alternate universe that is closer to the realm of a Star Wars crossover.
My reasoning is that the show goes out of its way to tie the Mane Six to their specific Elements. The flashback in the Season 4 opener shows that the Element of Magic looked like Twilight's cutie mark even when Celestia used it. Furthermore, the Season 5 finale made it clear that if the Mane Six had never become friends, they never would have become the Element Bearers. Not only that, but it seemed like no other Bearers arose to take their place. There must have been individuals who stopped some of the villains in each of the timelines, but no other group could stop all of them. This shows that the Mane Six are destined to save Equestria from Nightmare Moon and every villain who came after her, and they're the only heroes who could defeat all of them.
Season 7 added lore that strengthened the Mane Six's connection to the Elements. I think it's possible that only ponies who have an emotional bond with the Pillars of Light could bear the Elements of Harmony. Four of the Mane Six grew up hearing stories about their corresponding Pillars, which helped shape their values at a young age, and the remaining two (Pinkie and Fluttershy) quickly became invested in their Pillars' stories as soon as they heard them. With Celestia and Luna, it's a bit dicier, since they only knew one of the Pillars, yet were able to bear more than one Element. It could be that Star Swirl told them about the other Pillars so that the princesses felt like they knew them. Another theory of mine is that Celestia and Luna served as placeholder bearers until the True Bearers arrived. It may even be that in the alternate S5 timelines, other ponies were able to temporarily use the Elements, but they rejected these ponies after a while, similar to the way they rejected Celestia.
This makes a lot of sense.
I wouldn't go that far, personally. For one, the emotional ties angle isn't exactly a very exclusive filter, given how the stories of half the Pillars are cherished legends passed down since their banishment to Limbo, and the rest survive either as the half-remembered Mysterious Mask, in a form of ancestor worship in the town of Somnambula, or as the ever less obscure darling of unicorn academics everywhere.
As for the other bits, stars, especially six-pointed ones, appear to be a universal symbol of magic in Equestria. At the very least, Shining Armor or Sunset Shimmer could've borne Magic. As for the alternate timeline argument, it actually paints a very stark image of Equestria. If these are the sole destined bearers of the Elements, accept no substitutes, then the stability of the country hangs by a thread. Six points of failure, any one of which will cascade into complete vulnerability to otherwise unassailable threats, to say nothing of what might have happened if the rainboom never came without cross-temporal interference. (And who's to say no other foals were inspired by the cross-country shockwave?) And it leads to the question of just how villains were defeated in the splinter timelines, especially since Nightmare Moon was thwarted in all but one or two of them. Does Celestia have alicorn-killers on hoof at all times, just in case? Heck, in Discord's timeline, Luna was right there with her sister. How?
Granted, I'm arguing from a biased position. To put it bluntly, I don't want this to be true, not least because alternate timelines are kind of my thing. I like to think Harmony and destiny are a bit more flexible than what you propose.
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That's a good point. Certainly the denizens of the town of Somnambula felt a stronger connection to that Pillar than Pinkie Pie did. But I do think it's significant that the Bearers were so driven to retrieve the magic-infused artifacts and free the Pillars, and darn all the consequences. However, they felt this way long after the Elements chose them. Of course, I may be reading too much into this because of my own preferences. I've seen at least one fanfic where Twilight is the immortal Bearer of Magic and the rest are just expendable, interchangeable sidekicks, and it rubbed me the wrong way.
As for NMM being defeated in all but one or two of the alternate timelines, another group of friends may have been able to use the Elements to defeat her, but then they drifted apart and the Elements rejected them by the time Discord came along. If nothing else, the episode makes it clear how important this particular group of six friends are to the fate of Equestria. In some of the timelines, three to five of them eventually became friends, but never all six. So these three to five of the "official" Bearers may have been able to thwart NMM, perhaps with help from other ponies.
Plus, having the fate of Equestria always hang in the balance supports the Benevolent Chessmaster Celestia fanon that I'm so fond of, although I realize the fandom is split on this interpretation of her character.
I should also point out that I don't think Harmony is so inflexible that it would want to make everything static and uniform. It's focused on destiny, but only in the sense that certain ponies are destined to defeat or reform major villains. Harmony requires different notes working together to form a composition, not just one note.