THE ONLY REAL THREAT TO WINDOWS IS: (Score 1)

The only real threat to Windows is something like an "MS-Linux with WINE exstensions", where the extensions would be trade-secret protected (Linux embraced a la Kerberos). Why is that so? Because if one is a keen observer of the past, one will find that the only way Windows overtook DOS is because it would run EXISTING DOS programs. The way windows is cathedralized, only MS can produce effective extensions to LINUX where Windows programs would run well. Then no one would hesitate to swith to Linux the new, the more powerful. It's for certain that they would protect those extensions. Notice also that double-booting, the current approach is complicated for most users, and that booting a system takes a lot of time, let alone double booting: shut down one, and then boot the other. (Ask and find out how many times a day people double-boot). Only Wine, running well, will do it.