I think you will see 3D destops in Linux before windows becuase of
If you do, it will be simple because there are a lot of programmers who are experimenting with it in Linux as shareware/open source.
There is no "resource issue" between any of the modern OS's that would make any one of them more or less suitable. OpenGL, DWM/DirectX10, and the OSX graphics libraries (old and new) are all more than capable of hardware accelerating these operations.
And there will be little or no hit to the CPU, unless the interface uses a lot of physics (like bumptop), but A) modern CPUs can handle these kinds of calculations without breaking a sweat, this is a perfect use of extra/multiple CPU cores, and C) modern GPUs have physics acceleration capabilities now (re: PhysX).
Trust me, ALL of the major OS vendors are working on 3d desktops.