The first conclusion that many people will jump to is the announcement of Fallout 4. Yes, this could be a possibility, and considering all of the hype surrounding the rumored game so far, it would make sense.
The strange thing is that no matter how large a game Bethesda has announced, we've never seen a press conference as large as Bethesda is making their upcoming E3 conference to be.
Whilst it is planned for E3, the actual conference will be happening a few days before all of the chaos of the gaming show. The event will take place on a Sunday, on June 14th.
Before we straight up say it's most likely to be a Fallout 4 announcement, let's take a look at a few other things Bethesda could potentially show off. Firstly, the Doom reboot we've all been expecting for a long time still hasn't showed it's face - that's one possibility.
If it's not Doom, Bethesda could release their upcoming free to play shooter BattleCry, but we doubt that game would receive a large press conference like the one planned for E3. A new venture into the Elder Scrolls universe could be a possibility too, but it would be odd for Bethesda to release a new Elder Scrolls game before Fallout 4. We'll let you know more as soon as we know more.