Like many comic book characters, simply lifting a costume design from the source material into a live-action adaptation may not work or make sense within the context of which the story is taking place. Case in point: The X-Men and the major changes in costume design from books to movies.
That being said, sometimes it can be done right as we saw with Zack Snyder's Watchmen. But what will director Joe Johnston do to include, introduce and utilize Captain America's iconic costume design? He does have an idea for how to bring in a character costume that's designed based on the nation's flag into the movie but it's not something we've ever encountered in the comics.
LA Times' Hero Complex interviewed the director yesterday and here's Joe Johnston's explanation:
"The costume is a flag, but the way we're getting around that is we have Steve Rogers forced into the USO circuit. After he's made into this super-soldier, they decide they can't send him into combat and risk him getting killed. He's the only one and they can't make more. So they say, 'You're going to be in this USO show' and they give him a flag suit. He can't wait to get out of it."
He continues to explain how this plot point was obviously never in the books because in the comics it was unneeded and it makes sense for heroes to sport extreme costumes. In a major motion picture, this has to be introduced or explained so it makes sense within the realism of the movie and for the suspension of disbelief of mainstream moviegoers.
"It was never in the comics... because they didn't really need it. In comics, he puts on the costume and the reader just justifies because of the nature of the medium."
I know there will be hardcore fans upset at this idea but I can see both sides and understand where Johnston is coming from. They do have to explain why the heck Steve Rogers would wear this thing during the war. However, what the director said later on the subject in detail may concern fans even more.
We know Cap will be a super soldier who they don't want to waste, so they throw him in the United Services Organizations, the group responsible for entertaining and boosting the morale of soldiers overseas during wartime. This is how he gets the costume, but what we can we expect from his involvement in USO exactly?
"So he's up on stage doing songs and dances with chorus girls and he can't wait to get out and really fight. When he does go AWOL, he covers up the suit but then, after a few things happen, he realizes that this uniform allows him to lead. By then, he's become a star in the public mind and a symbol. The guys get behind him because he embodies something special."