Good day,
Asside from the fact that that is extremly hard to do (virtualization is very hardware specific), it would be extremly hard for a project like Whonix to create a secure implementation of said virtualization like Qubes has done. Adding to that a “Whonix only OS” would require a custom desktop enviroment, to accommodate the multiple VMs based concept.
Regardless of the fact that that is very subjective and debatable, that wouldn’t be legal either due to copyright laws.
Have a nice day,
Ego