Or worse, the OEM's void your warranty if you try to install vanilla Windows to avoid it to lock you into their solutions. I realize there are implications to some of the above that would break software, but we see the same things across Linux distributions all the time. Why would open sourcing Windows be any different?
Windows could never be open sourced anyway. There is code for libraries and other components licensed out from other vendors and all kinds of patent mess that would make it extraordinarily difficult for them to do it anyway. Its a cool thought, but its also a can of worms I hope they don't open.