WARNING: LONG, YET INFORMATIVE AND SPECULATIVE POST AHEAD
Other than Richter, each of the newcomers so far had Ballot speculation presence to varying degrees (yes, even Simon). Sakurai even mentioned that Chrom and Dark Samus had many requests, which is a big reason they are Echoes (and Daisy as well, retroactively).
Hell, even some of the new ATs were relatively recurring names thrown around.
PLAYABLE FIGHTERS:
-Ice Climbers
-Snake
-Wolf
-Pichu (yes, Pichu was a semi-common topic; far more so than Squirtle or Ivysaur)
-Young Link (same as Pichu, though mostly for a revamp using masks)
-Inklings
-Ridley
-Simon Belmont
-King K. Rool
-Daisy (Echo)
-Chrom (Echo)
-Dark Samus (Echo)
ASSIST:
-Waluigi (was already an Assist, so not that big of a deal as an Assist compared to the others)
-Bomberman
-Krystal
-Knuckles
-Shovel Knight
So I've been compiling a list of
other "hot topics" of the Ballot days to varying degrees to see what characters we could probably see being fitted into either role.
-Banjo-Kazooie (Would be either playable or not in the game at all; can't see Assist being an option in this particular case.)
-Isaac (Could return as an Assist like he was in Brawl if he is not playable.)
-Paper Mario (Could be playable, could be new Assist, could be just a trophy again.)
-Sceptile (Could be a new Poké Ball summon if lucky; very questionable of an inclusion overall due to circumstances such as Gen. 7 being on the way when Ultimate started development.)
-Shantae (Like Shovel Knight, could be an Assist if not playable. Or a trophy. Or not in the game at all. -shrug-)
-Impa (Could be a possible Sheik Echo)
-Dixie Kong (Could be a regular newcomer or could be a Diddy Kong Echo)
-Rayman (Could be
anything, really. At least he was a trophy before... -shrug-)
-Crash Bandicoot (-more shrug- Not sure what to think.)
-Skull Kid (Could be playable; for whatever reason we have a new Assist in the Moon from the same game, but not the Skull Kid himself yet...)
-Bandana Dee (Could be playable, could be Assist, could be trophy.)
-Sora (-even more shrug- Though seems like another "playable or nothing" type due to Disney's involvement.)
-Geno (Could be playable, could be Assist, which some might argue against.)
-Wonder Red (Another wild card that could be anything.)
-Chorus Kids (Who really knows their fate at this point...?)
-Goku (Manga/anime character, so odds of any sort of appearance is very low. But if there were any exception to that "other media characters" barrier, it'd be him. But don't bet on it.)
-Shrek (HAHAHAHA-no. Shrek is a much harder sell than Goku.)
-Freddy Fazbear (One of the three major "meme" votes of the time alongside Goku and Shrek, but is arguably more plausible than the two given that the barrier for
him is "no Nintendo presence". Which
might not matter as much due to FNAF being a worldwide phenomenon, which yes,
includes Japan. Still wouldn't bet on an appearance, but it could happen for all we know, even if just an Assist role.)
Others such as Shadow (who was a bigger topic during the Brawl days) or Isabelle who I strangely didn't find much discussion of are still possible. Same with certain post-Ballot deals such as a Gen. 7 Pokémon (considering we have new Poké Ball summons from Alola).
This above list was just to cover the remaining "hot topic" names from that time period given that Ultimate seems to be incorporating as much of them as possible.
I may have forgotten or overlooked a few, so feel free to correct me if you feel I missed some big ones.