[1] http://blog.netbsd.org/tnf/entry/the_lua_scripting_language_in
[2] http://cvsweb.netbsd.org/bsdweb.cgi/src/share/examples/lua/?only_with_tag=MAINHonestly, I think I would rather see the userspace work out of core (ie: not shipping w/ NetBSD) and just put into pkgsrc (NetBSD version of Ports, or dpkg, etc) as a NetBSD-only package.
The kernel work -- I'm just not familiar with deep kernel hacking, so perhaps it's my ignorance, but an interp in-kernel doesn't sound attractive to me. I think I'd rather see kernel access pushed to userspace, like FUSE/PUFFS[1] does for filesystems, or even how procfs allows reading/writing kernel from userspace. Jamming more into the kernel, especially an interpretter makes me shake my head. It could be fun as a personal project, or a Clever Hack, but for a shipping production-ready system... reminds me of when RedHat introduced it's in-kernel http server[2].
All that said -- NetBSD is _still_ the most attractive Unix I'm aware of. I occasionally consider a Linux or FreeBSD, but haven't left yet, since NetBSD 1.6 (c. 2002)