You want a $1,000 Xbox?
Actually I might like it if they did make one, but it would have to be a system designed with the express goal of running games at 4K 120hz.
And that's a software goal as much as a hardware goal, but I'll put up the money if that's what needs to happen to get me there.
I've said it a bazillion times now, there is almost no game design on the market today that can't be done at 4K 120hz even with just modest hardware. The only reason extra high resolution and framerate aren't standard is that publishers like "cinematic" screen captures for advertisements.
Games running at a lightning fast framerate can't be demonstrated in TV ads, special effects can, and the unfortunate reality is that most games play worse because of it.
Moving forward developers really should be aiming to have a "smooth gameplay" mode alongside all the crazy shaders and such that publishers seem to require for screenshots.
Give me a "core" mode with stripped graphics and maximum display specs and I'll be a very happy camper.