Character creation, a longer post game and a true challenge like Necozma.
Yeah, it would also be a treat to battle other champions and gym leaders from other reasons. As well as have a legit and non-event way to finally catch mew and arceus...Exactly. This would be another great addition to the game. When there are more characters to play in the game, it definitely makes it a bit more fun and satisfying.
This is actually a very good suggestion mate.