Indeed.
No technical measures. (At most a hideable whonxicheck warning but I haven’t found ways to detect the host operating system from within VirtualBox VMs.)
Yes. It’s about what becomes the default choices on the website and what we are willing to support in the forums.
Also - if - this gets implemented - Whonix Windows Installer - Design Documentation might be resurrected and no more direct ova downloads. (Manual build of Whonix ova images for Linux would still be possible or extracting those from the Windows installer.
Debian based Whonix-Host-KVM and also potential sudo apt-get install whonix-host-kvm for Debian.