If they're truly sticking with OT characters, it's a short list.
Possible Heroes:
Obi-Wan Kenobi (would add variety in the form of a blue lightsaber but otherwise would be too similiar to Luke)
Yoda (not sure what playstyle they could use considering his age/ability in the OT timeline, this would be a horrible choice)
Chewbacca (his gun could basically be permanently explosive, this would be a great pick, but his hard to animate fur and the fact that the developers already said he was unlikely is a strike against him)
R2D2 (would play a lot like Boba Fett if he had his prequel jets and would add neccessary balance to the hero side in Heroes mode)
Lando (would play almost exactly like Han or Leia, an extremely unwise choice.)
Possible Villains:
Tarkin (boring dude with a blaster but maybe he could request orbital strikes idk)
IG-88
Those red dudes from ROTJ
One of the randos from Jaba's palace, I guess
Honestly the villain side is extremely lacking. If I had to give my most likely bet, it would be this:
R2D2, Moff Tarkin, Obi-Wan Kenobi and... maybe some new bad guy from Rogue Squadron. I really can't think of a second viable villain from the OT. :
edit: let me stress in response to posts on the last page that the devs already more or less confirmed that they aren't doing Chewie. I forget which interview it was, but they were pretty clear that it was something they wanted to do but weren't able to. Probably because of his hair! I wouldn't want to deal with all that either.