Transmission 1.50 has been released. To me, the most interesting part is "IPv6 support for peers, and for trackers with explicit IPv6 addresses".
Proof that it works: see the included screenshot of transmission connected to another IPv6 bittorrent peer, with happens to be a Vuze (formerly Azureus) 184.108.40.206 client.
Hooray! No more NAT problems thanks to IPv6! :-)