I'd really like there to be a plot that ISN'T a generic "evil team revives legendary Pokemon and things go wrong" storyline. We've had variations of that plot for 4 straight generations now, with some being better than others, and it always starts and ends in the same way. I'd really like something a little more complicated and interesting, sorta like Gen V's plotlines were.
While we're at it, it would be really neat to have a landlocked region. That's something we've never really had before; all of the regions seen thus far have been next to the sea and in at least three cases have been completely surrounded by water. It would be cool if we had a really mountainous region, with a lot of unexplored places where new Pokemon could be hiding around every corner. It would also be really cool to have the Battle Frontier back, and to possibly have a huge cave system of sorts a la the Underground in Gev IV.
In general though, there's two main things I'd really love to have in Gen VII. The first is a tiny bit more science fiction included. This may just be Final Fantasy VI and VII on the brain, but while Gen V dabbled in it a bit, there's never really been a Pokemon game where it was front and center. It would be really cool if we had a Pokemon game that actually centered on this. Of course you can't just have machinery without the lush and diverse environments Pokemon is known for. But the two games I mentioned balance nature and advanced science quite well. There's no reason Pokemon shouldn't be able to do that.
Of course above all, I'd like more polish. If there's anything I can say about Gen VI, it's unpolished. There's lag, bland and stiff Pokemon models, and with Kalos in particular there's a lot of linear routes and towns with absolutely no depth. That's just not how a region should be. Pokemon at least partially is about exploration, and nothing is worse than a Pokemon game that has nothing to explore. Of course a lot of polish is needed everywhere else, like for characters, the story, the models, the difficulty, the Elite Four... Instead they spent all their time on Mega Evolution. They didn't put all that much polish into that either, as they severely underestimated now many Megas there would be and just how overpowered some of them became. If it's one thing Gen VII needs to have above all else, it's polish. I can deal with the same plot over if the game is well polished.
