A list you can now subscribe to:
https://lists.wikimedia.org/mailman/listinfo/ee
Discussion of initiatives that support new users and experienced editors on Wikipedia and MediaWiki projects ("Editor engagement" & "Editor engagement experiments"). So, for instance, right now they're talking about Echo (the automated one-to-many notifications system), and I figure that they'll be talking about Flow (the user-to-user communication & subscription & commenting system that).
Added to https://meta.wikimedia.org/wiki/Mailing_lists/Overview#Interest_areas .