I don't have any kind of actual plot thought out here - I just want to see an AU where both Bucky and Steve fall off the train and get captured by Zola (say someone else stops Schmidt, like Peggy or the Commandos or whoever). So Bucky gets his metal arm and superhumanness and everything, maybe they keep Steve on ice in order to control him. Until everything goes wrong and they escape to kick ass.

I don't care - whatever you want, I just want to see Avengers/the Winter Soldier w/ Bucky and Steve fighting on the same side against Loki/Hydra. And while Steve/Bucky is preferred, it's not required.