Honestly, I'm betting Halo 6, a "look how great the Scorpio is!" presentation of Forza, probably some rough Crackdown footage with more cloud computing marketing gobbledygook, and another pinky promise that Phantom Dust is still a thing, no really. And probably more info on Sea of Theives.
Which is to say a very predictable E3. Honestly, at the moment it seems all their eggs are in the Scorpio basket.