Bethesda has announced that they will be hosting their own E3 conference on June 14, aka my birthday.
This announcement—which comes via their blog—brings Bethesda into the big league of publishers with their own E3 presser, joining the likes of Ubisoft and EA.
What Bethesda could announce, demo, and unveil is pure speculation. There is high demand for a sequel to 2012's Dishonored. And The Elder Scrolls Online will come to consoles around E3's time period which means that IP is probably out. Battlecry, an upcoming free-to-play online game, is the most likely to get some news.
A Fallout sequel announcement is the most coveted however, as rumors of the game and its setting of Boston have been rampant for the past year or so. It's possible that an announcement could come sooner though, with a reveal at PAX East in Boston, and a demo coming during their conference. Fingers crossed.