there's a few projects for running windows in a container.. winboat and winapps are a couple that come to mind. dunno if they're ready for 'prime time' yet. interesting concept, though.

Nope. Not always an option, for example, My recording studio is running Win10. I cannot get the same audio latency\performance I need in a VM, and some of my software will not even run if it detects that it is in a VM.

There's also things like HASP\Sentinel license keys that will detect VMs and refuse to run, all kinds of licensing servers do this to combat piracy.

I could go on... but I do IT for hundreds of businesses, I run into these niches fairly often when trying to virtualize legacy systems or retrofitting hardware for industrial equipment.