Another 20 posts has passed, and even though I haven't mentioned it before, I plan on doing some sorta crazy theory or analysis or something like that post every 20 days. (Last was "Who is Starlight Glimmer?", which landed exactly on the spot of the 21st post on this site.)
Now, I've mentioned it's a theory time post and since the title doesn't give any valuable information on the subject, without further ado, lets introduce the question at hand:
What is the destiny of Starlight Glimmer and Twilight Sparkle?
Now, what you may have noticed is, that Twilight decided to take Starlight in under her wing and teach her friendship, just like Celestia once did to her. Now, what was mentioned in the debate on what to do next with Starlight, it was mentioned that she's quite powerful, probably even more powerful than Twilight herself.
Which brings us to our first point,
Power & magic
Now, we can definitely say without a doubt that both Starlight and Twilight are one of the most powerful magic wielders in the land. And using our good old formula of
Friendship = magic
we can only assume that these two unicorns are the main ponies who should be studying friendship.
We've seen Twilight use a time spells, finish up and old spell and have an epic showdown with a beast. All showing her true power.
Then we have Starlight, the pony who (quickly) wrote up a spell to use the Cutie Map to travel back in time (and be actually able to alter it), magic hovering, stealing cutie marks and a lot of other great demonstrations of power to show her true magical capabilities.
Now that I put it this way, I can totally see how Starlight is more powerful than Twilight.
Anyway, I guess I've made my point, two of the most powerful ponies around.
Existence & time travel
Now this gets interesting, we've finally reached the crazy theory zone!
I'd like to start of by stating the obvious. So far, Starlight and Twilight are the only two unicorns that we know have used time travel spell. (There could also be the case of Starswirl the Bearded, but we don't know much about him. Furthermore, Discord is also believed to be associated with time spells, despite not changing past in them, so considering all the crazy Starswirl-Discord theories, we're gonna have to drop it until further information is received.)
Now, where am I exactly going with this? Well, the answer is, in a lot of different directions, but firstly, and most importantly,
Theory one (AKA The Sparks' first theory) : Starlight & Twilight exist outside of time-space continuum
That's right. Much like the Cutie Map, Twilight and Starlight seem to exist outside of time-space continuum. What exactly is the proof of that? I'd say, the lack of paradox in Cutie Remark. You see, Starlight and Twilight traveled back in time, altered the past and everything changed. When Twilight returned to different new timelines of Equestria, one thing to be noted was change around her. (And Spike. Seriously, I'm not gonna mention Spike tagging along with Twilight on the little time travel adventure, in this post, from here on out, as it contributes absolutely nothing to the explanation of the theory itself and would be just a waste of time.)
Now, even after all that had changed, something was still there, the Cutie Map. Throughout the entire adventure three things stayed the constant in the crazy mess that was going on with time:
Starlight, Twilight and the Cutie Map.
Cutie Map is part of the "Great destiny" playing out, so there's a reason for that.
But why were Starlight and Twilight there constant? Why didn't something in their personalities change throughout the course of the alternation of the timelines? Or why didn't it all just end in a mess of a paradox where an event in past prevents pony from coming from the future to make that event happen? It's simple, the unfolding events were a fixed point in, well, lets say "time" to keep it simple and from going over the top trying to come up with ways how to call it. It's the thing, much like the Cutie Map, both Starlight and Twilight exist outside of time-space continuum. None of the laws of time apply to them for that very same reason. Time in Equestria is linear, (taken from the fact that past can be altered, so it has to be linear) yet both Starlight and Twilight managed to break quite a few rules of linear time during their adventure. But even more oddly enough, Cutie Map was always there to follow them. We once again return to the point, where we have to say that the events of the Cutie Remark were a fixed point in time, playing part of the "Great Destiny" playing out.
And so far, there is reason to believe that Starlight, Twilight and Cutie Map are the key elements of that destiny playing out.
Alright, now for some fun speculation we can do with this theory. Starlight is Clover the Clever. We don't know much about Clover the Clever, other than the little play put on by mane 6, where the role was played by non other than Twilight Sparkle. We don't know the looks, most of character traits, none of that. All we know is that she was a unicorn (or perhaps an alicorn? We don't know what she could be hiding under that cloak.) living in an old time (Before Luna and Celestia) and introducing the magic of friendship first to the other ponies. Now this works oddly well if you take Starlight's ability to just warp between time and (upcoming) lessons in friendship into account.
What's more, perhaps she could be behind that time defying Luna-Celestia flag that they raised before the known existence of the first alicorn. And that adds another question of, could Clover the Clever be associated with the birth of the "first" two alicorns? Speculate in the comments!