Microsoft TV, beating Apple to the punch. With integrated Xbox functionality.
Besides they have invested a ton of money in the x360 and continuously push the x360's OS to handle media. Clearly they'd be stupid to release a TV that duplicates some of the x360 functionality. Nothing to gain.
I do wonder what they'll announce though.
I doubt that's actually what it is, though; maybe some exclusive content deal for Xbox and/or Win 8 media devices. The choice of LA as a place for the event kinda suggests that to me. I'd assume it's entertainment related, in any case.