I created a global USE flag for memcached, see some discussion here: https://archives.gentoo.org/gentoo-dev/message/235fa47b46dc6d5897bf7463c4f7bf44 In lighttpd, the USE flag is currently called memcache rather than memcached. It would probably be nice if you can rename it.
Assuming there are no objections, I'll be changing this USE for any new versions. I've not had much time to take a look at the package since taking it, but I'll do what I can tomorrow or Thursday since it's such a small change.
The USE flag has been converted starting with lighttpd 1.4.42. When it stabilizes I'm looking to clear old versions that've been monkey-patched. Marking as IN_PROGRESS and adding InVCS until 1.4.42 hits stable.
lighttpd 1.4.42 is stable, closing.