You know one of the great things about VMs? They're cross-platform. I'm guessing once the same amount of optimization is put into arm has has been put into x86, the performance ought to be comparable. I'm also about 99% sure docker can be run on arm (RPIs support it, right?).

With that said, I sincerely doubt Apple will kill x86 wholesale overnight. I'm guessing there will be a transitional period of quite some time.

Also, windows has been doing a ton of work around getting onto arm. I managed to test on my rpi 3, and it was pretty good. it would probably be very doable.