I went to Nintendo of America for play tests to find bugs, glitches, etc. Since I'm a close friend to one of the employees, him along with a Nintendo treehouse rep were pretty open about giving info about Super Smash Bros Ultimate. Since they didn't want to ruin any big surprises, I only got a little bit of info so here's what I know.
Characters
-Shadow (Echo Fighter)
-Chibi Robo
-Square Enix rep(TBA)
-Pokemon rep(likely to be Decidueye)
Stages
-Fountain of Dreams
-Hanenbow(I don't blame you if you forgot about it, so did I)
-Crisis City(unlocked along with Shadow)
-Friendly Fields(Star Allies)
Music
-Twilight of the Gods(Remix)
-Scuffle with Torna(Remix of Torna boss theme)
-Snake Eater(Remix)
Items
-Blade Core
-Paraglider
-Chef Kirby's pot(works like brawl final smash)
-Cape (Double jump into damaging glide like brawl)