Thegameandwatch
Smash Ace
My opinion is that if it’s similar to Smash 4 then the number of old characters in the full reveal wouldn’t be that much like how Brawl only had 5 in E3 2006 while Smash 4 only had 9 in E3 2013.If there's not a teaser, I expect more like Smash 4 where we get a reveal in the initial trailer and one in a separate trailer right after the fact, like Villager and Mega Man.
Probably the main ones from franchises that are first/second party (generally 1-2 each) although not all them.