That's why KB/M should be moved to the domain of Windows software. I expect it's the same as the VR situation I've talked about elsewhere. MS could do with XB having access to the same Windows Store content, but I guess they haven't got that on XB1 and will bring it in for neXtBox. Then they can have dedicated, optimised XB software, and a true Windows shell or however they do it for supporting Windows content but walled off to only run Windows Store bought games. Anyone wanting KB/M games will be able to play them as if using a PC and buying through the Windows portal. Controller based console-fair can be sold through XBox. Players can be segregated based on what platform they are playing through, with Windows on XBox having a different player base than Live games on XBox, but of course it'd be the same account, shared across devices, with content bought on one working on the other. So you could buy a game on XBox, play online with controller, connect a KB/M, and boot up the game in Windows to play int PC mode against other KB/M players. It'd be a nice stepping stone to usher people more towards Windows as an entertainment platform.
A technical hurdle preventing this happening on XB1 is the only logical explanation I'm happy with. MS already has KB/M games on Windows Store, wants to encourage people to use Windows Store, could trivially support KB/M on XBox, but it's not happening. Same as VR on XB1X - MS only need make the headsets run and make the games available. So I'm guessing XB1 isn't able to run Windows stuff seamlessly yet. Play Anywhere titles appear to be few and far between, whereas transparent execution of Windows titles suggests every Windows game could be added. That may of course be business decisions on the part of the devs/pubs though.