Bring back some of the older generation Pokemon. Possible choices could be the first to fifth generation starters. Like, after you beat the first gym, you get to choose one of the starters from the first generation. Beat the fourth gym, you get to choose one of the starters from the second generation. After the sixth gym, you get to choose the third generation starter, 8th, the fourth generation starter, and after the Elite Four, you get to choose the fifth generation starter. How would that go out? Your team in the game will probably be really high level by then, but you could use the starters for the after game unless you wanna have the EXP Share on it while you're in the Elite Four, but that's no fun. What do you guys think?