My guess is they're going to announce a way that Xbox and PC are connected under Windows 10 (perhaps a UI revamp for XBO?) or I could even see something crazy like if you own an Xbox One you can play games on your PC from it, kinda like remote play but a PC instead of a Vita. Maybe this year they'll actually follow up on saying they haven't abandoned PC gaming, in Phil Spencer we trust.
I think you're on the right track. A complete revamp and restructuring of the Xbox One UI to synchronize with Windows 10 (maybe it will even run Windows 10!) is probably what we will be seeing, along with DX12 coming into play on maybe one or two fall games. The all-seeing cloud will help both PC and Xbox to talk to each other and stream back and forth like nobody's business.
P.S. Any news on Metal Gear Scanlon 3? After playing MGS3 over the holidays I'm geared up for some more!