Nothing known about Smash.
Mario Kart 8 Deluxe includes characters not in MK8 like Squid Girl and Squid Boy from Splatoon, King Boo, Bowser Jr. and Dry Bones, revamped Battle Mode with new arenas like Urchin Underpass (Splatoon) and Battle Stadium with old ones like Luigi's Mansion (GCN) and Battle Course 1 (Snes), 3 new karts, items like Boo and Feather were shown off in the Battle Mode, two item slots instead of one, and there's this Smart Steering feature they posted about on the website that is suppose to allow people to stay on the track easier.