A lot has happened in the Samba4 world over the last week.
Andrew Bartlett has got a simple domain join to a Samba DC using kerberos working using a hacked-up version of Heimdal kerberos. He's now looking at the best way of doing a KDC for Samba4 - either writing one from scratch, borrowing one from one of the existing open source implementations or borrowing parts of one of the existing ones (a "libkdc"). There's been some heated discussion about this on the related mailing lists.
I have merged pidl2 (my rewrite of pidl, our IDL compiler) into the main Samba4 SVN branch. This is something I have been working on for the past 2 months.