http://git.tuxfamily.org/gzc/completion.git To get the tree :

git clone git://git.tuxfamily.org/gitroot/gzc/completion.git

Here is a git ebuild but be warned: you'll install the HEAD git revision so you can be 99% sure that something is broken.
That said, if you feel lucky, go ahead with this ebuild and report bugs to help us :)
http://download.tuxfamily.org/gzc/zsh-completion-99999999.ebuild

Gentoo zsh completion currently implements the following functions :

• write a git ebuild, for dev and testers.
• cleanup the code : try to write every function with the same way of coding
• split _portage in :
  • _portage (for programs that come with the portage pkg)
  • _baselayout (for programs that come with baselayout)
• clean up all functions removing the obsoletes programs
• complete _eselect by adding per-function completion, keep the actual way to do the completion for others. here is a list of existing completions for eselect
  • bashcomp (included in eselect) – do we need that one?
  • binutils (included in eselect)
  • ctags (eselect-ctags
  • env (included in eselect)
  • fontconfig (eselect-fontconfig
  • java-nsplugin (java-config)
  • java-vm (java-conifg)
  • kernel (included in eselect)
  • mailer (included in eselect)
  • news (eselect-news)
  • oodict (eselect-oodict)
  • opengl (eselect-opengl)
  • profile (included in eselect)
  • rc (included in eselect)
  • vi (eselect-vi)
  • blas (eselect-blas)
  • cblas (eselect-cblas)
  • emacs (eselect-emacs)
  • esd (eselect-esd)
  • gnat (eselect-gnat)
  • lapack (eselect-lapack)
  • oracle (eselect-oracle)
  • pythoon (eselect-python)
  • rails (eselect-rails)
  • timidity (eselect-timidity)
  • vdr (eselect-vdr)
  • wxwidgets (eselect-widgets)
  • xvmc (eselect-xvmc)
• _gentoolkit :
  • add function for eclean-dist
  • add function for eclean-pkg
  • add function for epkginfo
  • add function for eread
  • add function for genpkgindex
  • add function for glsa-check
  • add function for revdep-rebuild (99% done (see ) @kaworu – should be fixed need testing @bapt)
• _gentoolkit-dev :
  • add function for ebump
  • add function for echangelog
  • add function for ekeyword
  • add function for eviewcvs
• _portage-utils :
  • add completion for q
  • add completion for qpkg
  • add completion for qtbz2
  • add completion for qxpack
• _portage :
  • add completion for emaint
  • add completion for env-update
  • add completion for portageq
  • add completion for repoman
  • add completion for tbz2tool
  • add completion for xpak
  • add support for sets
• _eix :
  • clean _eix()
  • add completion for eix-diff
  • add completion for eix-sync
  • add completion for eix-test-obsolete
  • add completion for eix-update
  • add completion for eix-remote
  • add completion for eix-layman
• add completion for sandbox (badly documented, so won't be done until we have enough information on the sandbox options)
• rewrite _gentoo_packages we would never use cache, so it is not necessary to keep it so complicated.