Might be a bit late to the party here, but I did have a thought about AVENGERS and RSDR filming, with Mr.Evans having such long hair and the beard... if Steve R. is still on the run for part of the movie, that would be where T'Challa/etc. would be involved, so it might makes sense that he's got longer hair, the beard, and supposedly (since Steve is blondish) dyed in order to avoid easy detection. OR it could be something that happens afterwards, when the Infinity stones have wrecked some havoc. And that way he wouldn't have to shave or cut his RSDR hair for AVENGERS.
Personally, I like the new look with the beard and the hair (I admit, I especially like the hair). I wouldn't mind if he did that hair more often between movies or in movies. Looks much better than the extensions he's worn in the past. Long live the long hair!