That can only happen when those other OSs match the level of functionality, reliability, and support that windows enjoys. I would love to switch my main OS to a Linux distro but it is still unstable enough and not supported enough that I can't reasonably switch.
As far as I can tell, our best hope is for Linux to improve at the same rate or faster as it has over the last 5 years for at least the next 5. Only then will Microsoft start to face any meaningful competition in operating systems.
