Basically, this is not about operating system kernel but about the notion of running a single process with somebody else's PAAS, which runs an actual operating

Basically, this is not about operating system kernel but about the notion of running a single process with somebody else's PAAS, which runs an actual operating system with a kernel and virtualization layer. Doing this on bare metal makes a lot less sense because then suddenly you need to worry about managing all the hardware, initializing it, dealing with file systems, storage, memory and all the other stuff that operating systems tend to do (or at least orchestrate). Modern VMs on the other hand don't really need to do any of that and simply hand off that stuff to the underlying OS via kvm or some other virtulization API. You could do all of that in your unikernel on top of bare metal of course. That's what embedded software manufacturers of course do. They build firmware that goes into a ROM and the embedded hardware boots the firmware. That's a classic unikernel. I guess some network router manufacturers might do something similar though most of them seem to like running linux or bsd variants and not reinvent a lot of wheels instead.