Re: Captain America 3 = Cap's Kooky Quartet?
I definitely like the idea of Cap 3 featuring Hawkeye, Quicksilver & Scarlet Witch. While I understand the apprehension of shunting aside existing supporting players, I think that the core Avengers team needs more of a build-up especially since they aren't going to headline their own movies. I do think it's possible to include them without sacrificing too many of the supporting players though. I don't think it would be a stretch to see Cap, Sharon, Hawkeye, Falcon, QS & SW up against a roster of villains like Zemo, Strucker (depending on what happens in AOU), Crossbones & Sin as they attempt to rebuild HYDRA. You could even use Sharon as an extra field commander in case you'd need the heroes to split up - something like Cap/Falcon/SW and Sharon/Hawkeye/QS.
Now without having seen TWS and knowing exactly where that leaves Bucky, I can imagine that him staying out of the action with some soul-searching would be an acceptable way to limit his involvement. You could still make him a central figure (but reduce his screentime) in the plot though - maybe the heroes need to seek him out since he has some information about a MacGuffin that HYDRA is after and that's how he ties in to this movie.
Sure, having all those characters in one film may limit some character progression, but allowing them to interact on-screen would at least give us some of that through team-building. Is that too much of an Avengers-lite scenario though? Even if it feels that way, do people care as long as Cap is the centerpiece? Maybe after seeing TWS I'll come up with some kind of treatment for a Cap 3 movie to expand on these thoughts.