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Change up the starters in some way. More than three choices, different types, odd type combinations, starters not based on animals, split evos, or even something like that speculated leakmon that changes types. Just something new and surprising.
Also, a PC dex to switch your party up on the fly. And opponents with enough mons to make your choice of six feel meaningful and at least a little strategic. And if gym leaders and elite four members must be themed by type, include more exceptions like in RB/DP. But different themes, like fighting strategy, design, color, etc. would be even better. And a qualifying tourney for the league a little more than halfway through the story would be a cool touch.