One thing to consider is that while almost all the games will be coming to PC, XBO-X will still be, by far the cheapest method for people to play those games on a 4k TV. Now, whether that's a factor or not is obviously debatable. But with TV manufacturer's pushing 4K HDR TVs, it's certainly going to ride on the coat tails of that to a degree. Throw in UHD BD playback, again debatable whether 4K UHD HDR movies are going to be a big thing or not, and the value proposition for the XBO-X isn't that bad.
I personally, don't see anything that would make me buy an XBO-X, but then again I have a couple thousand USD invested into a PC. And I'll be investing another 500-700 USD soon for a Ryzen upgrade in order to ensure 4K playback.
IE - a LOT more expensive than XBO-X. I'd imagine a lot of people that buy a 4K HDR TV might find the XBO-X interesting.
Regards,
SB