...Are we still talking about a pony MMO? I don't know about it being set during the "Nightmare Moon Era" cause that can only go on for so long until NM gets sent to the moon. Plus if it were set in the "modern" Equestria you'd get the chance to take quests from the Mane Six, and wouldn't Hasbro want them showing up in the game in some form?
That said, I do love
The Old Republic even though I know no matter what I do,
Alderaan will blow up, the then current Empire will lose the war and it will all become the prequel movies.
I guess I'll throw my idea on classes. Basically I think they can get away by combing race and class, and each race gets tank, healing, & DPS spec
Earth Pony
Soldier (Tank) | Medic (Take a guess) | Ranger (DPS)
Pegasus
Storm Guard (Tank) | Weather Pony (Healer) | Daredevil (Rogue-style DPS)
Unicorn
Royal Guard (Tank) | Sage (Healer) | Wizard (DPS)
I hear there's a Transformers MMO in the works based on
Transformers Prime,
Transformers Universe. Its possible if
that becomes a success, they'll try to apply the formula to their other franchises like
G.I. Joe and of course
My Little Pony.