MLPPP is vastly, vastly different than IPv6. Absolutely no way IPv6 going into 2.0. If someone provided a patch today that fully implemented it, it would be held in a git branch until 2.0 is released. That touches every single portion of the entire system and would delay the release considerably, which we're not doing. Adding MLPPP affected nothing other than PPP, and nothing with PPP aside from MLPPP configurations. That was a hundred lines of code across two files - IPv6 would be thousands of lines across hundreds of files. We already added way too much to 2.0, nothing major is going to be added until post-release.
If someone wants to start a clone in git and start working on it, more power to you! By all means, please have at. People can run from that clone if they want. It's not getting merged til post-2.0 though. You have to draw the line on releases somewhere or they'll never get released. The line on 2.0 is drawn.