The next version of systemd (215) will include udev rules which assign a group 'input' to devices added under the input subsystem. Given that we include groups like audio, video, and disk in baselayout, it would seem to make sense to include 'input' as well.
Not meaning to divert the topic of the bug, but upstream also removed the floppy group at the same time: http://cgit.freedesktop.org/systemd/systemd/commit/rules?id=f31cf2b6d03a18e4f8f52214c1a3ffa9b3c97189
Sorry, I don't want to diverge either, but to prevent anyone from mistakenly dropping the 'floppy' group from baselayout -> I've restored the floppy group udev rules in 40-gentoo.rules at sys-fs/udev, there was no reason to drop it for non-systemd systems
This is added in commit f25b3db and will be included in baselayout-2.3.