My top 5 wants:
King K. Rool
Dixie Kong
Skull Kid
Ray MK III
Isaac
My top 5 predictions:
King K. Rool: I think that almost everyone expects him. Why else would they suddenly make a character from a bygone era a costume? He always scores high on online polls, and although those may not be the best samples, I still think it's noteworthy.
Dixie Kong: In my eyes, Dixie Kong can get in without King K. Rool, but the other way around isn't possible. I wonder if Sakurai would ignore Dixie Kong if he added K. Rool. She may not be as wanted, but she is still a very popular character who is relevant and easily implementable (Diddy Kong semi-clone or echo).
Elma: Sakurai seems to like Xenoblade, and it was probably too early for Rex and Pyra.
Mimikyu: An Alolan Pokemon who was purposely created and marketed to be popular. Honestly not 100% sure if we're getting a Pokemon newcomer, but if we do, it's him. Sakurai probably knew about the plan behind Mimikyu.
Chorus Kids: People are sleeping on Rhythm Heaven HARD. Sakurai probably told the Rhythm Heaven developers of his intention to add the Chorus Kids to SSB4. I feel any developer - especially smaller ones like them - would be ecstatic. For him to say that, then take them out, then not include them in a sequel unhindered by technical limitations would be a slap in the face. There were the Forbidden 7 in Brawl and Dedede/Mewtwo/Bowser in 64, but they were from huge series that already had playable reps. Rhythm Heaven still has nothing. I question if Sakurai would do that.