Would be waste of power in desktop PC's
Small tablets or phones would be the limitation for how powerful the system would be.
That wouldn't be comparable for how much power a workstation may have.
So for have a chance in take advantage from all the resources in our desktop computers there should be two different versions of Windows 8.
But if consider how much work that can be saved by only develop one version for them all, it wouldn't be unreal to believe that much of the time could be used for developing many more features instead. So I guess the whole discussion ends in 50/50 anyway:)