I'm pretty skeptical. First, it's rarely ever really one application. There's a primary application, sure, but there's also a bunch of processes that monitor it

I'm pretty skeptical. First, it's rarely ever really one application. There's a primary application, sure, but there's also a bunch of processes that monitor it, clean up its logs, perform system maintenance, etc. Second, you lose 100% of the tooling for debugging. Finally, and most importantly, your operating system does an awful lot of stuff that is not trivial, not in the slightest. The Linux kernel has better page cache algorithms than your unikernel, a better networking stack, vastly better hardware support, etc. Plus tons of people thinking about how to make it better every day. No one is going to port that to OCaml.