Haven't speculated further than hoping certain characters would come back (wanted PT/Squirtle and Ivysaur back more than I did an actual newcomer, Snake coming back over any other third parties, etc.) in a long time. The only obvious ones I wanted this game were in fact Inkling/Ridley (and Simon Belmont to go along with that rumor), with Krystal being my pipe dream (happy she's an assist done in her classic look/with her staff).
Guess if I had to pick some on the spot in particular order, I'd go with:
Dark Samus (Echoes be damned/go for broke with doubling the Metroid representation)
K. Rool (I'd say it's time)
Spring Man (DLC if nothing else I'd love a stage/music from the game)
Rex/Pyra (see above, though I'd prefer them over Elma for base roster)
Bandana Waddle Dee (also say it's time)
Dillon (don't expect it, but I love the concept of Dillon vs Sonic which even the creators of his game would love to see)
Tingle (based heavily on his own games, plus to go with the above comment, the same interview also mentioned SUPER TINGLE)
Shantae (any indie rep would be awesome though)
Ashley (we lack a true witch playstyle, plus if it meant more remixes of her theme, I'd be down)
Medusa (goes nicely with both more villains/females, she was in the original KI, plus it would be awesome seeing the inevitable tie-in/reference if Simon gets in)
Honorary mentions -
Dixie Kong (Echo Fighter wouldn't do her justice, IMO)
Kamek (if Yoshi needed a new rep, not a priority in my eyes)
Linkle
Shadow the Hedgehog (the only Echo that makes sense/came to mind immediately)
Doomguy (hey, we got Ridley)
Crash Bandicoot/Spyro (didn't grow up with them, but would be neat all the same)
Geno (for the whole dreams coming true thing going on)
10th Pokemon (really I can't discern/say I'd dislike any of the current popular choices, I just don't prioritize them between "playable fighter" and Pokeball)