I see that this topic has been popped up from time to
time since 2004,
and that most of the misc servers have been already IPv6 enabled. I
have checked around whether google have any info on that, and found a
few (really few) mail on that, from the original 2004 test to a
comment from 2008 that squid and mediawiki is the problem, apart from
some smaller issues. (As a sidenote, google don't seem to find
anything on
site:lists.wikimedia.org about "ipv6", interesting.)