I want microtransactions, QTE's, paywalls, unpolished gameplay, simplistic and patronizing tutorials, unskipable cutscenes, lengthy loadtimes, and for it to be published by Ubisoft.
Developed by Imminent Uprising.
If I'm expected to take this remotely seriously, however, I'd struggle to find an appropriate place for MLP to fit itself into. A game directly involving the Mane Six would definitely be the most successful and probably the only viable course if they want to turn a profit (and they do), but I feel that such a premise would limit what the developers could do while keeping it within the realm of MLP. I'm thinking it would have to skew more towards an older demographic (not bronies specifically, but consumers who are readers of the IDW comics) in order to gain enough edge to work within the more action oriented genres that gaming lends itself to. A puzzle-platformer would be a very interesting route to take, and probably the smartest move. A Sonic Adventure style affair, in which each character has wildly different objectives and methods to get through the same set of stages would probably work. Twilight's new position as of the Season 4 finale does seem to function as a worthy excuse plot to get the action rolling at a minimum, although each stage could be a specific "friendship mission...thing" with its own self contained story. The introduction of new villains would be best so as not to conflict with the canon, although I'd expect one of them to appear in the show for cross-medium promotion. I'm not going to delve into mechanics specifically since there is any number of ways for them to go.
Genres like the action adventure or an RPG could possibly find a way to work itself into a worthwhile title while still pleasing Hasbro's PR and marketing teams, but I feel that the more action-oriented a game's concept becomes, the less likely it'll be greenlit.
And still put Imminent Uprising in charge. That'll be hilarious. Jim Sterling would have a ball. Which would also be hilarious.