grep, gettext, groff, texinfo, cvs, rcs, gcc, binutils are the big gnu things left.
replacing gnu grep and its many extensions in a compatible yet efficient way is hard. bsdgrep comes close but iirc is still lacking in performance. heirloom toolchest does not come close.
we need groff for building the installation notes and /usr/share/doc, it isn't needed for any man pages, where mandoc is used happily. not a big deal. part of the remit of netbsd is replicating the full CSRG distribution, including things like the berkeley vi tutorial. probably you do not have the same goals.
you can easily make netbsd build with clang instead of gcc, that is documented widely.
elftoolchain comes about 1/4 way to replacing binutils with a non gnu license.
texinfo, cvs, rcs you can probably happily purge
note that most of the GNU tools in netbsd (gettext, grep, etc) are the pre-GPLv3 versions