Trying to think of potential heroes and villains here from the OT that would actually make a lick of sense.
Heroes:
Ben Kenobi (Slower paced Jedi, maybe more ranged abilities, mind tricks to turn one to your side?)
Chewbacca (Gives them the opportunity to have an actual decent Bowcaster in the game, plus he could have some strong fucking melee)
Yoda (Although I don't want him, as he'd likely be wielding a lightsaber, and the Emperors moveset shows they aren't afraid to pull from the prequels, so it's actually very possible)
Lando? (Probably the worst suggestion, if they armed him, he'd just be Han from a gameplay perspective)
Villains:
I'll say up front, I think the Wampa is the best suggestion, which is a sad state of affairs, so without Phasma or Kylo Ren, villains are slim pickings.
Basically any of the Bounty Hunters (All great designs, they're vague enough to make them whatever you want, gameplay wise)
Greedo? (Again, not great but I can't think of anyone other villains that actually wields a weapon -- also his race is already in the game, so he actually doesn't really work at all even from a design perspective)
Someone suggested Jabba, he'd be super gimmicky, but if he was a more static character, it could bring something different to the table.
Heck, he's not really a villain, but running around beating people up as a melee / tank Wampa would be dope, too.