As an attacker I care only about the data and don't give a a shit if it is a real machine or a virtual one. If I can sniff the passwords in your browser or just have a keylogger in one of the VMs I am fine. Not sure if that solves a thing.
edit:
I remember there were similar concepts a decade or so ago. where you had your "green" desktop for intranet or whatever and then a seperate "red" desktop which you could switch to and go to the evil internet. hint: no benefit gained
edit: I remember there were similar concepts a decade or so ago. where you had your "green" desktop for intranet or whatever and then a seperate "red" desktop which you could switch to and go to the evil internet. hint: no benefit gained