The live site is now running the full type-safe TLS stack all the way down to the TCP/IP stack and Xen device drivers. If it feels a little sluggish from your browser, this is because TLS session resumption hasn't been merged in yet (but is available to test at https://github.com/mirleft/ocaml-tls/pull/283)
MirageOS, HHVM and learning how to build compilers have been my main impetus to learn Ocaml, and I'm glad I did. It's a lovely language, and now that mirage supports TLS directly it'll be an easier sell for certain tasks where I work, I'm quite excited!
I have seen bare metal options before, for example for Common Lisp, but this really looks good. BTW, does anyone have a list of bare metal systems like MirageOS for other programming languages?