>And if your emulator is too good, what stops ISVs from saying “you did it for us, we don’t have to care”? So once again they don’t have to do it at all and you have no native software.

x86 emulation enables adoption.

Adoption means having an user base.

Having an user base means developers will consider making the platform a target.

>Saying “Ha ha, just kidding, it’s RISC-V now” would be a disaster.

Would it now? If anything, offering RISC-V support as well would further reinforce the idea that Windows is ISA-independent, and not tied to x86 anymore.