it would probably end up being battlefield 1944, as battlefield 2 already exists and so do 1942-43
Whatever the name of the game is, that's gotta be the next logical step in my book. 2009 was the last Battlefield game to be during WW2, which by 2017 will be 8 years ago. I played BF1943, and from what I remember it was a very simple game, but still fun. Before that, it was Battlefield 1942, which is already 14 years old. I haven't played or heard of a big budget FPS game set in WW2 with the kind of large-scale battles, destruction, graphics, and team play like anything Battlefield does.
It also makes sense from a business standpoint. I don't like comparing games, but BF has the upper hand over CoD big time. I think it's the perfect time for a WW1 game from BF. EA DICE knows they would be super successful making a WW2 game with the tools they have today, but I think it's a smart move to save that for the future and release Battlefield 1 this year when they know people are going to buy it. They're set up very well right now in my opinion.