Yes, Smash is a crossover, obviously. But (a) once they started doing these character-specific reveals, they stopped revealing multiple characters in the same trailer unless they're related (Palutena and Dark Pit, Robin and Lucina, Simon and Richter); (b) revealing multiple characters in this manner steals the thunder from one of them; and (c) even if both those things change, any third-party character will get their own, singular reveal trailer. Look, as much as I love Skull Kid, he doesn't stand up to the weight a third-party character carries.
Villager and Mega Man have separate reveal trailers, just played one after another in the Direct.