I'm inclined to think that Bucky will be back, alongside the introduction of Sharon Carter. Confident that Fury will put in an appearance.

I think Hawkeye, Black Widow, Arnim Zola, Red Skull (in some fashion) and Dum Dum Dugan are all in play. Baron Zemo is also a possibility. Wouldn't be shocked if somehow the "Truth" storyline is incorporated. (I'm imagining Cap learning more about the extent of the Super Soldier program as he learns who's still alive in the present day.)