I think the hardware support point is moot because if Windows did switch to Linux (Microsoft wouldn't but we are playing the "what if" game here) then hardware manufacturers would obviously port their drivers to Linux else nobody would buy their hardware. We've already seen this to be the case on Android for example. Plus Linux already has reasonably good support for older hardware.

I should stress again, just in case anyone misinterprets my comment, that I don't for one second think Microsoft will not should switch to Linux