Ah so thats cool that Mona is playable. She was cute.
I really do think the next character will be an indie rep. Nintendo is pushing indie games HARD, and they are even sponsoring the indie showcases at TGS. What better way to show indies are important to them then giving them a smash rep?
The list of viable indies are not huge but a decent size.
Shantae: probably the biggest indie studio out there, wayforward has a lot of clout on the indie scene, even if they mostly take a back seat of it. They have been around the longest, and have worked on the most games. Shantae is a spirit already but i still dont think that disconfirms someone being playable. Shantae also has a long history on nintendo, so she is one of the top choices.
Reimu Hakurei. The queen of the japanese indie scene, touhou project is by far the biggest doujon game series in japan. Its representation on nintendo is only newer, but one cannot argue the impact on japanese gaming society touhou has had. It wpuld make a lot of sense to put Reimu into smash for those reasons. Plus her unique bullet hel mechanics could be interesting in a smash setting.
Quote/curly. Cave story is one of the oldest and well known indie games out there and having them in smash would be a huge honor and could be feasible since the series has a long history on nintendo.
Fisk. I will admit i never got into undertale, but i cant deny the inpact it had on the indie scene. Plus it sounds like sakurai is a huge fan of the series. I dont want an undertale rep myself but i can see it as a chance.
Hollow knight/Hornet. Nintendo is pushing this series hard, and it was award winning. Also old enough and has a new game coming, both important factors i feel for an indie spot.
Honestly those are the indie reps i feel really have the best shot. Candance is still a little too new i think? Next game i can see her easily happening, or as a second rep.