My understanding is that Window NT (back to 4.0 at least) was already that. A Windows GUI running on top of a UNIX or UNIX-like kernel. Win XP was then built on top of that. This whole thing is really about killing your competitors using the force of law rather than competing.
Could be, could be. Maybe Windows sucks despite having a unix kernel under the covers, not due to lack of one. Certainly, the unix kernel doesn’t appear visible in any user or programmer interface or control. If it’s under the covers, it’s under lots and lots of ‘em.