Version 1.6.4 is here. There is basic support on enough plugins that we can upgrade now.
So next time you join the game make sure you click on Edit Profile in the bottom left corner and then select 1.6.4 in the Version drop down.
If you are using Magic Launcher then click on Setup and then Browse for the new version. After you find 1.6.4 in the Versions folder save the setup and then launch the game.
I will get some pictures up to document this process eventually.