The tree is now public:
http://mysql.bkbits.net:8080/mysql-6.0-ipv6/
There are some issues with Windows that I need to resolve (which has more to do with broken Windows setups then problems in the code).
Instructions on how to build from Bitkeeper from here:
http://dev.mysql.com/doc/refman/6.0/en/installing-source-tree.html
I still need to change the family defines to allow the IPV6 pieces to work, but that is just a couple of lines. I wanted to get the refactoring out of the way before I did that.
The tree is an Alpha, so don't even think about putting this into production environment (as always, I recommend people stick to GA releases for production usage).