interesting, although the old mantra of "hardware is cheap, developers are expensive" is still true. you could hire 10 perl/c/c++/javascript/php/etc dev with ease for your project, but struggle to find one ocaml dev. And even then your ocaml dev will need to know the mirage library, xen and have a good knowledge of way more stuff than your project scope

that said, it's still really cool, but it's not something i'd use, and especially not in production

There is nothing stopping people from implementing something similar in other languages.

The developer using this doesn't need to know anything about Xen, they just see a single address space system that runs their code.

for Erlang, there's ErlangOnXen: http://try.erlangonxen.org/zerg

There are others, if you care to search for them.