I'm not really writing this to impress or persuade anyone, I just wanna get my thoughts down and see what others think of it. I hope it all makes sense/hasn't already been covered.

Before I begin, I just wanna say: Wow. If you had asked me a couple of years ago if I watched MLP:FiM, I probably would have given you a weird look. I saw how popular it was on forums and stuff, but I couldn't understand why so many people my age were into it (since I thought it was just a show for little girls). So I gave it a shot, and to my surprise, I fell in love too!
But still, until recently, I haven't analyzed the show like this. I guess you could call me a late bloomer in a lot of things, and becoming this hooked on the show has just recently hit me and made me start thinking about it in more depth. I even created a pony OC (or 3, hehe) and developed a strong desire to go to BronyCon. Maybe it's because the show just keeps getting better and better to me? I have fallen in love with a certain awesome draconequus, and if it weren't for him, I may not be as enthusiastic about the show as I am now.
Also, all this headcanon stuff might make more sense if you knew my headcanon of Discord's past - if you're interested, just let me know and I'll give you the link. :3

So here's what I've been thinking about:

Anyone ever notice that when Discord used his magic to pull the mane 6 to him by their element necklaces, his magical glow was yellow like Celestia’s? Maybe I over-thought it, but...
I like the idea that popped into my head when I connected those two yellow magical glows, and it’s not like he can’t have light and dark magic, since in my headcanon he was once an alicorn (and also because chaos isn’t an entirely bad thing). If I recall correctly, Celestia and Twilight also use dark magic at some point.
So I connected the color of their magic by thinking that Celestia is the spirit of harmony and Discord is the spirit of disharmony, so essentially they are two sides of the same coin and are incomplete without the other to balance them. I like to think that both spirits of harmony and disharmony appeared not too long after the birth of their world.
I don’t see chaos as a bad thing unless it’s unbalanced, which is what had happened to Discord after he had originally failed to make friends in his younger years. He’s the spirit of chaos, and when he failed to find balance through connecting with the ones he was surrounded by, he became out of control. Until finally, Celestia (I won’t mention Luna because she doesn’t help me make my point and it’s already been shown that Celestia can handle the elements on her own, as well as handling the sun and moon, only making my belief that she’s the spirit of harmony stronger) shows up with the Elements of Harmony and puts chaos on hold until the world recovers from the chaotic overload and balances out again. But since harmony and disharmony already live inside everything and the actual embodiments are meant to act as equalizers, I like to believe that Discord had been temporarily drained of his power when they first turned him to stone (since it was the elements of harmony they used against him), and that he had spent all that time slowly rebuilding it until the CMC’s little argument provided him with an extra boost that sped up the last small portion of his recharge, and he finally broke free.
And of course the first thing he does when he breaks free is unleash all the power he’d been building up, but after the second time he’s turned to stone, Celestia says she can find a use for his power if it’s used for good instead of what she considers evil and decides to unleash him again. She knows that as the embodiment of chaos, he can't just be kept in stone forever or else the world would end up being imbalanced again, and that he’s not all bad if he stays balanced and satisfied. With all that magical power, he has the potential to do a lot of great things, like re-capturing Tirek. But since her plan to use him that way backfired (since she was taking the still-unbalanced spirit of chaos and mixing him with another unbalanced source of disharmony), maybe that would be a clue that only the friendship of Fluttershy was just a tad too weak to prevent another imbalance, since she is only one part of six that make up friendship/harmony. Discord needed to befriend all of the mane 6 (or, since I think she’s the spirit of harmony, Celestia herself) to be balanced, and if he had done that before Celestia tried using him to put Tirek back in his place (the way she expected the mane 6 to handle it), maybe he wouldn’t have been so easily persuaded, meaning that he was still imbalanced because only one part of harmony (kindness) had tried to connect with him. So she blames herself, thinking she had put too much trust in "reformed" Discord. The other Elements had failed to show him what their parts of harmony meant, especially Rainbow, since loyalty was the main thing he lacked. So I blame the mane 6 minus Fluttershy for his betrayal.
But now that it seems like he’s finally learned what friendship/harmony is, I hope to see more of truly reformed Discord taking on tasks from Celestia the way she employs the mane 6 to do things to help keep balance in Equestria. Maybe he can even officially begin to help Celestia continue to teach young Princess Twilight - he’s been doing a good job of it so far, even if he does go about it in a different way. I think he’d make a great advisor (or even future king ;D) for Celestia - spirits of harmony and disharmony working together to keep balance. They'd be quite the dynamic duo. It’d be perfect!
Celestia herself I think is kind of underrated, and she deserves more screen time. Whatever they do with that, I just really want to see a relationship between Celestia and Discord grow, hopefully into something romantic one day. While I don't see anything really romantic in the flower-giving at the end of S4 (since in my headcanon they've never had a romance before), I do think it's super cute and it could be the start of a great relationship. In my head, they have the potential to work very well together (their relationship would be much more interesting than Fluttercord, and they'd probably have an even stronger bond IMO, not to mention the strangeness that I've considered in Fluttercord's age difference, especially when considering their human forms, so I hope they stay just friends), and I think there is just too much potential with this couple for the writers to ignore it. Hopefully you'll agree, and thank you for reading!

3624127 Interesting, I've never noticed the golden magic bit before. Nice headcanon you have going.

Oh thank you, I'm glad you liked it!