Someone (I forget who or where, the tab’s just been open my background for a while) recently posted a link to an old blog post about “Qubes Air”: Qubes Air: Generalizing the Qubes Architecture | Qubes OS
Much of it is focused on the cloud use-case (while still giving users control over exactly how much of their system is cloud-based, and supporting things like “local clouds” hooked up via LAN), but the section on “Qubes Zones” and the following section “Under the Hood” seem particularly relevant to your questions. They talk about some of the changes that need to happen/requirements that need to be implemented in order to use a different “hypervisor” (or some other equivalent technology, like cloud APIs).
Unfortunately, per Updates on Qubes Air? - #3 by fepitre, the QubesOS team does not have the bandwidth to actively work on the required architectural changes at the moment.