Xbox One VR category seen on official E3 website
Several companies have a new category listed on their E3 website pages. This category is shown as "Virtual Reality > Xbox One", effectively confirming the possibility of Xbox VR products being shown at E3. So far, 4 companies have added this category to their pages, including Rebellion, Maximum Games, 3DRudder, and Readily Information Company. Between this and all the recent rumors, it would be very surprising if some kind of VR headset or software for the Xbox One was not shown at E3.
Source - Rebellion
Source - Maximum Games
Source - 3DRudder
Source - Readily Information Company