I just got done playing a bit of the Titafall Beta and wanted to post here to confirm that 21:9 works perfectly in the game. Here are a few screen caps to verify.
The 3D aspects are rendered perfectly at 2560x1080, but like many games, the HUD is completely screwed up. In fact, most of it is missing. Setting the HUD margins to "LARGE" helps a little bit, but even then, about half of the HUD edges seems to be messing. This is especially noticeable when the com-vids pop-up and half of the characters face is missing. So yeah...hope they fix this before the game is released.