That's what I thought too, but it looks like it's just getting restricted to private groups and disallowing media/content uploads.
It's probably to push people off so they can shut it down later.
i would assume it's an anti-spam effort
All messages will stop on Yahoo groups (last one of the bullet points.)
It will just function as an alias for all that group members. Yahoo won't save the email on their servers; instead, expands the blah@yahogroups.com to every member, and sends them a copy. That way, they don't need to maintain any infrastructure besides email server.