From the Ethos homepage...
> "The solution to both of these problems is Virtual Machines (VMs). Since VMs allow multiple OS to run on a computer, it is no longer necessary to choose one OS; multiple OSs can be used simultaneously. Hence, one significant application can justify running an OS. Second, the VM provides an abstract hardware architecture which is far simpler then the vast variety of computers extant. The drivers for the real hardware are provided by the VM. We are using Xen as our VM because we believe it is a good security architecture on which to build an OS."
So the plan is to run on baremetal hypervisors like Xen, just like MirageOS and the rest.
> "Ethos has an interesting capability and crypto model that unikernels could map their distributed communication primitives too as well."
If that's the main aim, then I don't see why they don't build their capability/crypto model into one of the unikernel OSes, specifically one of those that has the strong type safety and process isolation they are also aiming for. I don't see what they gain from having a custom OS requirement when a lot of the groundwork has already been done for them.