I also don't see any problem with the WMF hosting a mailing list--we have a number of locally user-based email lists for entities which have no interest in forming a chapter (Wikimedia-sf to name one) and I see no problem with the creation of a Wikimedia-man-uk (or something like that).
It sounds like this is intended to be something broader than Wikimedia. Is the WMF happy to host mailing lists for general free culture stuff with no direct connection to Wikimedia?