User blog comment:Jenburton/Coming Soon: Message Wall in Labs/@comment-1073312-20111024231431/@comment-1656630-20111024231829

We intend to send out a sitewide notification about this feature with appropriate warning time to all users before anything goes live to all wikis, but that's not happening right now.

Also, talk pages will not vanish. They'll just be archived. You'll always be able to get that information.