Currently /usr/share/dict/words files is available from sys-apps/miscfiles package. Unfortunately miscfiles repository looks dead. On the other hand many users who care about spell checking already have aspell/hunspell installed.
Some modern programs rely on /usr/share/dict/words file for spell checking (for example https://github.com/git-cola/git-cola). It would be nice to install a more modern dictionary for such programs and to avoid pulling a collection of antique BSD files. We can generate this file from installed aspell/hunspell dictionaries.
ArchLinux distro uses aspell dictionaries to provide such file (see https://www.archlinux.org/packages/community/any/words/). A similar approach should work for hunspell (there exist a bugreport regarding this on hunspell sourceforge page, but the site is down atm).
We can refine ArchLinux approach: generate words file for each lang in LINGUAS, then put a symlink to the first one, which is considered default (ArchLinux generates words files for a limited numbers of languages only and determines the default one based on the LANG value).
I can work on the needed additions for aspell and hunspell packages if someone is interested.
But I don't see how to resolve a conflict between aspell and hunspell if we choose to generate words files for both of them.
Also http://wordlist.sourceforge.net/ project exist, which provides a limited number of words files and is used in Debian.