databeestje's IPv6 branch is the way to go. It will be in 2.1.
That said, the underlying binary software is the same on both - the daemons (like OpenVPN, DHCP, etc) for IPv6 support are all there. It's just the GUI bits and related functions that aren't in 2.0 proper. That's why it's so easy to overlay databeestje's code and have it work without any hasstle updating to a custom firmware image or build.