I'm not sure if this has been metioned before, but what I would like to see in the new CMS is subsite abilities.
I think about something similar to the oacs 3.2.5 homepage module, where every user could create his own homepage whithin the installation and publish it under a certain url.
It would be great if a user could say: I would like to use your full featured CMS to create and manage my private pages and folder structures. Additionally I would like to use your templating system to make it easier to streamline or change the appearance of my pages. On top I could enhance my "new homepage" with other oacs modules like forums or news etc.
By the way: Some days ago I heard about Yahoo's SiteBuilder... http://webhosting.yahoo.com/ps/sb/
Maybe they have interesting new features or templates that we could use somehow...