We are removing some of the completions installed by bash-completion, and I'm thinking of extending that list. Here's some bug to collect ideas for what should be removed.
1. cal dmesg eject hd hexdump hwclock ionice look ncal renice rtcwake
Those were removed originally because they are included in util-linux now.
2. explodepkg installpkg makepkg pkgtool removepkg upgradepkg
Those are Slackware packaging tools. I doubt someone is using them on Gentoo and the names are generic enough to collide. For example, sys-apps/pacman installs makepkg (yes, we need to teach Arch not to use generic names as well).
3. ifdown ifup ifstatus
That's some fancy Debian/Red Hat stuff. I don't think they are useful for Gentoo.
4. arch (and possibly other mailman tools)
The bash-completion's 'arch' tool is for mailman arch and not coreutils arch, so it collides hard. Another thing is that our mailman tools are installed in /usr/lib*/mailman/bin and the completions rely on mailmanctl being in $PATH.
Nothing is happening here for a long time.