I would sell my Xbox, if KB/M support is not added for the base X1.
KB/M will be added for the X1 - they've already said as much previously as I understand it.
However, I think there will be restrictions on how and when you can use KB/M vs controller, much like their currently is with Rocket League. In Rocket League, you can either opt in or opt out of playing people on PC vs Xbox only. I believe they will implement a similar solution for FPS games like Halo. You will not be able to run around dominating with a KB/M vs people with a controller. Or I should say, all of the controller people will simply opt out of playing against KB/M people because of the inherent advantages of a keyboard.
Unless all your friends also plan on migrating to play on PC with KB/M, you could be trying to build up a new player base of people to play with.