This will go great for DC.
In case you hadn't heard, DC is currently trying their hand at the shared universe Marvel has essentially perfected with the upcoming Man of Steel sequel Batman vs Superman. Originally scheduled for July 17, 2015, DC moved the film to May 6, 2016 to avoid competition from Marvel's next big films Avengers: Age of Ultron and Ant-Man. The catch? May 6 was also the date of an, at the time, yet to be announced Marvel film, with DC seemingly trying to get a small win on Marvel by forcing them to move that release date.
And yesterday, months after the date swap, Marvel has accepted DC's challenge. The unnamed Marvel movie set to be released on May 6, 2016 will now be... Captain America 3. The Winter Soldier must be really, really good. And, now it seems, the best course of action for DC is to move their release date to late that year. Because, really, this is a win-win for Marvel. There are really three scenarios that could play out here.
First, Marvel wins the weekend and Batman/Superman comes in second to Cap 3. That would be a major boost for Marvel and would essentially kill any plans DC had for a Justice League movie. When all three of your biggest characters lose to a, at least for now, second-tier character, it's best to start from scratch. Again.
Second, DC wins weekend, Batman/Superman in first, but Cap 3 comes in a CLOSE second. Here, the likeliest scenario, Marvel scores another success while taking a chunk of what DC could've gotten, a chunk they can't afford to lose. If Batman/Superman made $120 million in it's first weekend, while Cap 3 gets $80 million, that's $80 million that likely would have gone to DC.
And finally, DC wins weekend, Batman/Superman does great and Cap 3 does poorly. Likely, Cap 3 will make up for a bad first weekend overtime, but Marvel probably doesn't care too much about sacrificing the Captain America series, probably because this third one is going to be the last one anyway. And DC still loses money that could have been made. And Marvel gets an excuse for why Cap 3 fails. Yeah, it's a bad day to be DC.
And honestly, Marvel's earned this. If the two films keep the same release date, which one would I see? Well, both most likely. But I would see Captain America 3 first, because, for now at least, DC still sounds like they don't know what they're doing with Batman vs Superman. I look forward to Captain America 3. I want to be how badly Batman vs Superman turns out, at least until better news comes of it. You move, DC.