Oleks

FiM definitely addressed some things too late or even didn't address them at all, like the origins of Zecora that have now been explored in the comics (yes, I now they had plans for it in the show that didn't get approved). Other things, like most of the Pillars, were addressed only superficially. And Twilight becoming an alicorn is an example of FiM concluding an arc too early and too hastily. At the same time some things they did address were pleasant surprises to me. For example, I didn't expect to see an episode about AJ's parents or the conclusion of Lyra and Bon Bon's background story. Also, Twilight and Shining recognizing Spike as their brother, and not just Twi's assistant was something I never expected them to address.

I agree with everyone who said "Big Mac", but I'd like to add an honorable mention: Doctor Whooves. He went from a random background pony to basically the Doctor in a pony from, and he even had a background relationship development with Roseluck.

My guess is they are teenagers, definitely younger than the Mane Six. Although it's based mostly on Sunny's room decor and badges.

Twilight: the type that usually says “I don’t have time for games”, but when tries one, can get addicted and wants to complete everything with 100% results. Pinkie Pie: casual gamer, plays for fun with friends, always accidentally finds exploits. Rainbow Dash and AJ: compete with each other all the time, probably mostly playing fighting and racing simulators. Fluttershy: that EG short pretty much sums it up, but possibly also a fan of survival horrors. Rarity: played The Sims once, spent 4 hours customizing her character. Spike: switched to single player games after Shining beat him all the time in multiplayer as a kid. Prefers tabletops anyway. Starlight: a fan of old school turn based strategies that no one knows about, finds it hard to find someone to play with. In RPGs always cheeses as a mage.

Limestone Pie. Didn't like her at first, but now she is my favorite Pie sister. Also, speaking about things beyond the show, Tempest Shadow. When I saw her for the first time, I hated her design and expected an edgy OC-like creature, but she turned out to be my favorite MLP movie character in the end.

Someone has already suggested that in terms of personality Izzy could be Pinkie + Rarity, Sunny – Twilight, Zipp – RD, Hitch – AJ, and Pipp – Fluttershy. But all of this based on only several images and a few seconds of animation. I personally would like each of them to have some unique traits, not found in any of the Mane 6. As for the origin of the Mane 5, my favorite headcanon so far is that Hitch is a descendant of Snails.

There's at least one in FiM: Silver Script and Star Bright: Plus, the one in Equestria Girls was confirmed by a show crew member, if I recall correctly.

I'd like to see everyone but humans in G5. Diamond Dogs would be particularly interesting to see. Maybe also sentient deer from the comics, although it would contradict the show, where deer are just animals.