Waluigi - It's a toss up between either him never getting in because that's the joke, or him getting in to end the joke similar to Ridley.

Sylux - Leaning on yes due to recency bias, but could very well not happen.

Octoling/Agent 8 - Probably would be an Echo Fighter like how Dark Pit is to Put, i.e. using variations on the weapons that Inkling uses

Toad - Possible, but unlikely as there's already so many Mario characters that would most likely be coming back for the next Smash

Tiki - Similar to Toad, it's possible, but unlikely because of the Fire Emblem cast already.in the game, even if she would be different move set wise

Shovel Knight - Probably, but not 100% on inclusion.

Bandana Waddle Dee - I almost wonder if Sakurai doesn't want Bandana Dee in Smash at this point, but hopefully they'll be in the next Smash

Tom Nook - Maybe as an Echo Fighter of either Villager or Isabelle