The problem is that the phrase used in Popek's paper is "Conventional OS". This was the 1970s. What's now considered a "Conventional OS" was not conventional

The problem is that the phrase used in Popek's paper is "Conventional OS". This was the 1970s. What's now considered a "Conventional OS" was not conventional back then. For instance, everyone would agree Linux is a conventional OS but Linux provides a kernel module (KVM) that allows for virtualization driven by userspace.