Turning Down the LAMP: Software Specialisation for the Cloud talks about how their team wrote a kernel (“Mirage”) to sit right inside Xen (as an OS) to execute OCaml in the entire 64-bit address space.
It’s a great article, so check it out. This is where I’m most interested in seeing new operating systems development and research going—desktop OSes have too much history, too many interfaces that need to be supported, all in the name of backwards-compatibility and pleasing consumers. But there’s much to be said for server OSes and research!