What I'm looking forward to is more detailed character models. Since the game already runs at 1080p/60fps, they'll have a ton of overhead.
And since character models are typically done at a high level of detail, and then scaled back to a level where the game runs smoothly, it shouldn't be much work to go back to the originals and create better quality assets from them. I'd be very surprised if we don't see that.
Can't wait for that higher quality Jigglypuff model.
I feel like we're at a point where they have a neat art style that works for Smash. Maybe upgrade some of them, but I don't think Kirby has had much done to his model since Melee.