The Win8 Product Teams have started blogging about new features in the upcoming Windows 8 release.
Windows 8 Server:
Microsoft Server and Cloud Platform Blog
Windows 8 Client:
Building Windows 8
Not so much out there for public details on the new Windows 8 Active Directory features so far unfortunately.
Best bet for the impatient AD admin is to download the developer preview version of Windows 8 Server and whip up a new forest in a test lab.
For further details check out the excellent compilation of other Windows 8 links on http://blogs.technet.com/b/askds/archive/2011/09/17/windows-8-for-the-it-pro-the-new-plumbing.aspx