> I guess one benefit of Mirage's use of the OCaml module system is that we can experiment with multiple deployment approaches and use whichever one works best in practice. So there's nothing stopping me from running a Mirage application on Linux with raw sockets rather than as a Xen unikernel.

That insight is spot on. The reason we're spending so much time on the clean-slate MirageOS stack is that it's a codebase that will last the test of time. It makes it possible to build code that's more future proof against changes in deployment environments. It's Xen/KVM/vSphere today, JavaScript and Docker tomorrow, and probably Unix sockets forever, all from the same codebase. Our use of OCaml + functional programming also had a good trajectory with practical formal verification, so the future of the stack is exciting.