I'd like to see them change things up a lot with this Smash, but with a 2018 release date it makes me wonder how long they have been secretly working on this. How much can we really hope for?
Skull Kid would be a cool addition. Luigi, but more Luigi's Mansion themed, to separate him a bit more from Mario's moveset.
Granted, people do seem to get upset when their favorite characters play differently in new iterations (unless it's to their favor), so Sakurai & Team probably have a hard time making those types of decisions.
I play Smash almost every day with my co-workers, even if just for 15 minutes. Every so often we'll have a tournament. Sometimes it gets competitive, but mostly it's just for fun. I play Captain Falcon and Ganondorf, mostly.