First and foremost, make some excuse to ditch Glimmer. That's going to be number one priority to get pretty much anything done. Now, a lot of ideas that could've been suggested in the earlier days on mlp, for example an adventure shift, have been completely fucked. Equestria has an established rule of no cohesiveness, if that makes any sense. All the neat places people had interesting headcanons about have been at least vaguely visited and unanimously they have been ruined some way or another. The universe is no longer mysterious and although there is zero aforementioned cohesiveness to their society, all the solid bits that we do have are boring and shitty, i.e, all the cities are at least in some factor generic modern-day styled, there's fast food & mega-corps, modes of transportation have been solidified, Celestia is retarded, griffons are unremarkable & worthless, stuff like that. So, with that in mind, I say the best option- not business-wise mind you, but in quality of show- the best option would be to go heavy-handed on not universe-building but the Slice of Life stuff. Now you may say 'but that's not the specific gimmick I wanted you to say', and I reply, suck my cock. Gimmicks ruin shows. They restrict them. This school will restrict the characters to, well, the school and school-related, student-teaching problems. And let me clarify, I don't mean rom-com sappy heavy-handed SoL, I mean day-to-day kind of open-ended stuff. Appul running her shop, with shenanigans that happen. Twilight has to chase down a book thief. Iunno. You get my point, though. Stray away from the hero role-model stuff and make the M6 likable characters again.