I have a really simple game idea for MLP:FiM, and it has to be on PSVita.
It'll be a 2D side-scrolling adventure that involves exploring all of Equestria and going on various quests from the townsfolk, missions from the Princess and fun mini-games around several locations. The game wouldn't be no small fry though. Story would last maybe the length of 8-12 EP's, all of which are original for the game, leaving the rest of the game for the exploration and several hundred side stories to get involved in.
The only characters available are the Mane 6, and background ponies would become available through DLC, specifically Derpy.
In contrast, it appears simple and short, but when you pick it up you are awed by the high quality vector-like animations, story telling and gameplay.