I use Parallels to work in Win7, I wonder if new MP’s will allow that if they are no longer Intel based?
But second, Microsoft has had Arm versions of Windows in house for a long time. They just never had a reason to release and support them. If Apple provides a mass-market Arm-based platform I've no doubt Microsoft and everyone else will make versions of their products available that run natively on them as well. At the recent iPad Pro announcements, Adobe, for example, announced that the full Photoshop will be available for it.
The bottom line is few users really care about computer instruction sets these days. That's just not a relevant decision point any longer.