Gentoo now has
up that describe how to get Gentoo/NetBSD going. The plan
seems to be to boot from a live CD, and then install from
that, mostly by extracting a 80MB .tar.bz2 file.
I still have no idea why anyone would want to do this,
and having a way to have a NetBSD base system and add
things via portage (just like what pkgsrc does) seems more
useful to me, but well.