Nobody has confirmed it outright, but all the evidence seems to be there: given that he's signed a contract tying him to a potential 9 MCU movies, it's obvious that Sebastian Stan - who plays Bucky Barnes AKA The Winter Soldier - is being groomed as the next Captain America. After all, Chris Evans has stated his intention to bow out once his contract is up (he has 2 movies to go), and Barnes ascended to Captain America status in the comic books after Steve Rogers died. All the pieces are there, and the fact that Stan has signed such a huge contract with Marvel just kind of confirms the studio's intentions for the future of the franchise. Shame, then, that Stan is a pretty boring actor, and that the Winter Soldier is about as exciting a villain as Thanos; which is to say, he's not an exciting villain at all. If this is the actor that Marvel have chosen to groom for the next generation of Avengers... well, it's not looking good. No offence to Sebastian Stan, but right now he comes across as another Kit Harrington or Sam Worthington; dull, dull, dull. Right now, he's not "important" enough to classify as a major weak link. Considering the future of the franchise, though, there's a lot at stake - and Stan seems like an odd fit as both hero and villain.
Sam Hill is an ardent cinephile and has been writing about film professionally since 2008. He harbours a particular fondness for western and sci-fi movies.