During the presentation at D23 Expo, the biggest thing that seemed to surprise fans in the footage for Avengers: Infinity War was that Steve Rogers had a beard. It's pretty safe to assume that since the last time we saw him, he left the shield with Tony Stark (Robert Downey Jr.) and busted his friends out of prison, and that he's not going to be calling himself Captain America — at least not for a while. It's not hard to picture what Chris Evans would look like with a beard…he grows one all the time. And a mighty fine one at that.
He has a beard that even Jonathan Frakes would be jealous of. But the question is, will he have another identity when Avengers: Infinity War starts? There are references in Spider-Man: Homecoming to a new shield, but Steve and Tony aren't on the same side yet. It's possible and likely that the film will start with another uniform and name and then pick back up the shield at the proper dramatic moment.
Steve Rogers has had many aliases over the years. If you look at Marvel.wikia.com, you get this list: Winghead, Shield-Slinger, Sentinel of Liberty, the Living Legend, Nomad, the Captain, Buck Jones, Roger Stevens, Yeoman America, Crossbones, Expatriate, Brett Hendrick, Nathan Hale, Anthony Schwarz, Roger Grant, the Man Without a Country, Lord of the Frozen Ice, Blondie, Granny, the Brooklyn Project, Weapon I, Super-Soldier, Rembrandt, Eagle, Subject 223, Spider-King, Cap-Wolf, Nova, Kapitan Amerika, Supreme Leader, and Hydra Supreme. Some of those may be completely made up…I have no idea. But there are two that would be worth looking at closer.
The first time Captain America walked away from the role, he took on the mantle of Nomad. He felt he was a man without a country or a home. This was part of the original Secret Empire story, and though he didn't wear the outfit long, he did pass it on to another former Bucky: Jack Monroe, who would continue on as Nomad for years. He even improved on the costume, which it desperately needed. They could go with this, give him a black-and-yellow uniform not too different from his Stealth outfit, maybe add a couple throwing discs. But I think taking the name Nomad would lead to some backstory that a film with so many heroes may not have time to build up.
This takes us to the second time Steve Rogers gave up being Captain America, this time for a different reason. It was decided that Rogers had never been discharged from the service, therefore he was still an active soldier and duty bound to follow orders. Rogers couldn't do that blindly anymore, so he gave up the role of Captain America, which then went to John Walker (later U.S. Agent). Rogers took on a modified black, red, and white costume and called himself The Captain, carrying an adamantium shield.
This seems like the most logical and easiest solution. Alter the color on his costume, but keep the same basic look, throw in a beard, and he's not Captain America anymore. Have someone try to call him that, and he can cut them off and say, "It's just Captain now." or "Captain will do." No setup needed. If they still want him to have a shield, he does know the guy whose country produces all the vibranium… and he was just there to drop off Bucky.
At least, that makes the most sense to me.