I'd love to see it. Though if the package is just "we run sel4's cmake script and save the result" then its much less interesting. If you can make a package which doesn't use cmake at all, email me. My email is in my bio.

Yes, for now the approach is to provide simple programmatic interfaces over CMake and friends to make third party stuff easy to integrate. For example, SQLite:

  spn_autoconf_t* ac = spn_autoconf_new(dep);
  spn_autoconf_add_flag(ac, "--disable-tcl");
  spn_autoconf_run(ac);
  spn_make(dep);

That being said, I'll have a go at sel4 with the native build system. I use it for all my C projects already. Nothing tastes better than dog food, after all!