All sys-kernel/*-sources IMO should have "doc" USE flag, and with "-doc" it should remove dir "Documentation".
Uh, no?! If it should be used for anything, then it's dependency on linux-docs, not for removing plaintext docs shipped w/ kernel.
Documentation takes unnecessary 9,4MB of disk space, docs would be better optional rather than obligatory.
Sorry, we don't want to cut this out from the ebuild side, you are obviously welcome to do it yourself. Also consider that there is a lot more than documentation in there, it includes scripts for downloading firmware and stuff like that.