So, as so often happens here on these interwebs, some folks heard a tongue-in-cheek comment and ran with it as gospel. A few months ago, the writers behind the critically-acclaimed Captain America: The Winter Soldier, made a remark about something that could appear in the next Cap film. Screenwriter Christopher Markus mentioned the storyline from the 1950s where there was a psychotic Captain America- a guy that turned out to be so obsessed with Cap that he actually had plastic surgery to look just like him- in an interview. Some places ran with this as a possible storyline for the third film.
Comic Book Movie had the chance to ask the writer, and his partner Stephen McFeely, about this recently, and they were all too happy to squash that rumor:
"McFeely: [Laughs] Chris, would you like to put that to bed?
Markus: Yes! That was a smart remark, off the cuff. What I love about that whole run, the whole existence of that, is the sort of single minded desire to retcon everything into continuity, you know? 'But there was five issues in 1950 where he was a jerk!' I know he was a crazed college professor who had plastic surgery, but I think we can honestly say that he will not be making an appearance.
McFeely: You know, there's probably 20 minutes of movie there. There's something interesting about a guy who so desperately want to be [Captain America] and be a tribute...I just don't think it's a whole movie."
So that settles that. If it does end up happening at all, it'll just be a small subplot- perhaps referenced in dialogue as an easter egg. That wouldn't surprise me, since the writers now know that it's on the minds of the fans.