future versions of Windows would have to be "fundamentally different" in order to take full advantage of future CPUs that will contain many processing cores.The concept of an "operating system" generally will have to change, even go away. Think "system" in a way that is unconfined to a "box" somewhere.
So, yeah, Windows would have to be "fundamentally different". It's not about "cores". Any specific silicon wafer will be just a host to *some* of the processes in the system. The rest will be elsewhere. Who cares, unless your revenue stream is an "operating system"?
If you are going to fundamentally redesign your system, you'd better aim for a technology landscape that is further than five years out. Ten years out will probably be as different to five as five is to today.