At one stage there was talk that this movie would feature WWII flashbacks. They could still of course have them, just without Peggy; however, I'm inclined to think that this suggests that the flashbacks are looking less likely.
I think while fandom still thought/hoped Atwell would be back that those flashbacks would include her. Thus layering the flashbacks with different folks from the first film. Since the Winter Soldier is prominent it stands to reason that to snap him out of it, whatever the "it" will be for the film, flashbacks of him and Steve would still be a likely scenario if nothing else.