One thing I do actually see us getting lots of are newcomer series, because every newcomer has to come with a stage. Plus, we only got two new series in this game, the lowest of any Smash Bros. [64 added Mario, Yoshi, DK, Zelda, Kirby, Starfox, Pokémon, Metroid, EarthBound, and F-Zero. Melee added Ice Climber, Fire Emblem, and Game and Watch. Brawl added Metal Gear, Kid Icarus, R.O.B., Pikmin, and Sonic. Smash 4 added Animal Crossing, Mega Man, Wii Fit, Punch Out, Pac-Man, Xenoblade, Duck Hunt, Street Fighter, Bayonetta, and Final Fantasy. All Ultimate added at this point were Splatoon and Castlevania.] Characters who didn't need stages back when it was the advantage are now at a disadvantage. There will probably only be one character coming from an already repped series, so Zelda and Kirby should probably shoot for Wave 2/Smash 6 at this rate.
There are few first parties, if any, not already present in Super Smash Bros., meaning that I anticipate actually a primarily third party set of DLC based on Smash 4's (though that one seemed to be a Sakurai set).