My impression is that Microsoft are taking a very conservative interpretation of the x86 ISA patents (compared to e.g. qemu-user which has made this available f

My impression is that Microsoft are taking a very conservative interpretation of the x86 ISA patents (compared to e.g. qemu-user which has made this available for years now). Patents have a 20 year lifespan, most of the x86_32 ones have expired, but x86_64 is just barely still covered (the first publication was in 2000, and first commercial product was on AMD Opteron/Athlon64 in 2003). So it's probably just a matter of time before the userland emulation stuff is further extended, although we won't get anything newer than SSE2 for the same reason.