I'm sort of conflicted on the concept of Zola as a main villain. I don't think anyone really expected Zola to be anything more than a side-villain. I think most think of people like Red Skull or one of the Baron's when thinking of Cap villains. Toby Jones is a good actor, but I have trouble picturing his Zola (even turned into a robot) as the main villain.
Basically this. Sure Winter Soldier will be Cap's main adversary but I don't get how Zola could be the mastermind given the way he was portrayed in TFA. I mean I like the character he played but he was not nearly ruthless enough to be someone I could picture pulling off some elaborate scheme.