I guess the more realistic expectation for future Smash content is more online modes (communities and lobbies like others mentioned already) for both versions alongside 3-5 more characters (alongside Cloud). Plus some more patches making things more balanced and making the unlocking process of custom moves easier would be nice too.
Considering we got major representation from Capcom, Sega, Bamco and now Square-Enix, I feel that we will close off third party character with one from Konami or Ubisoft. The former already has a character that can be re-used from Brawl (Snake) while the latter while not friendly with Nintendo now, helped them out a lot over the decades (the GC era got many multiplatform games from Ubi, the Wii got a lot of support from them and they were early supporters of the Wii U before they cut their ties 2013-2014).
I could see Rayman really come to Smash (representing Western developers supporting Nintendo) but I could also see Shovel Knight doing that too (as it could representing Nintendo having strong connection to Indie developers.
Honestly thinking about it.....I could see the following join Smash with the final wave of DLC.
-Cloud Strife (Final Fantasy VII): Already announced but likely releasing in December after the Smash Event. Looks awesome and comes with the Midgar stage on Wii U (not sure if its coming to the 3DS version though, at least with the summon gimmick the stage has)
-Solid Snake (Metal Gear Solid): Look, Nintendo got Cloud in Smash (basically a PlayStation characters through and through despite it being a Square character), so they can get their other Sony guest star in Smash again too. If Nintendo is friendly with Konami (which they seem to be, considering all the GBA Castlevanna games coming to the Wii U E-Shop and being friendly in the past), then this is possible. Little work too, as they could re-use Snake's moveset and stage from Brawl as reference or port that over to Smash U/3DS. After Cloud's announcement, I'm almost expecting to hear about Snake next month

.
-Inking Girl & Boy (Splatoon): Big Nintendo surprise hit of the year and a prime Nintendo new-comer to Smash

! Really creative moveset and I could easily see a really great Inkopolis level join Smash. Hoping Iinking(s) come to Smash in the future

.
-King K. Rool (DKC) or Paper Mario (PM Series): I could see either join Smash but not both. This is likely the Nintendo Poll Winner, so they only have room for three (1 Nintendo, 1 Third Party, 1 Indie Character) winners. Both have a lot of moveset potential and each will add to the respective franchises representation (a playable rep for the Mario RPG titles or finally adding in a DKC villain into the Smash series). Could see them bringing a new stage (TTYD Battle Arena for Paper Mario or King K. Rool's ship from DKC2).
-Wolf (Star Fox) & Ice Climber: Both are bound to be coming to Smash in the future; both are similar to Lucas, Mewtwo and Roy (already having a base moveset to copy over from older Smash titles) and would be great to see them back

. Ice Climber can easily work on both versions; only have one of them playable but have their attacks have double impact (Ex: Down B has him/her using both hands for the ice blast, Up B has him/her throwing an pick-axe in the air and gabbling to it, Side B has him/her using two hammers for a spin attack, ect). Could see them launching with Cloud this December.
-Shantae or Shovel Knight: One of them representing the poll winners (Indie side). Both have a lot to pull with Movesets and both have great stages to use (Shantae: Scuttle Town with Risky shooting cannon balls into the town and tinker bats roaming around/Shovel Knight: Great Planes, Plague Knight's Lab or The Enchantress's Castle).
-Rayman: He could represent the third party poll winner (if Snake doesn't represent that) and his moveset is filled with potential across Rayman 1 (throwing fist, hovering in the air), Rayman 2 (Energy Balls, Stronger Hovering), Rayman 3 (Costume abilties, Kick attacks) and Rayman Origins/Legends (Dash Punch, Ground Pound, ect). The stage for him is tricky.....as you could have one from Rayman 1 (Glade of Dreams), Rayman 3 (Land of the Livid Dead), or Rayman Legends (any location).