I am thinking that, eventually, we will have VMs running in windows, too, just like Wine does now. Think "super crazy .app bundle" where you double click the image file, it launches the guest OS, boots, launches a single application, and then makes that app fullscreen and looking like a normal window.
Some trickery would be needed for device access, saving and sharing files, etc., but these are solvable problems. The end result would be desktop app isolation, extreme app portability (I can emulate any platform anywhere, in theory) and if you made the iconify button suspend the guest to disk in whatever state it's in at the moment you could carry your work--exactly as you left it--anywhere with little more than a flash drive.
Once this is happening who cares what data centers are using virtualization for!