We have been working off of a 0.4.0.1 branch. There have been some minor fixes (such as the JAMA User-agent work) and more recently I rewrote the Crossref package to use the new crossref api at api.crossref.org/works on our end.
The initial version freeze was motivate to promote stability on a codebase we weren't all too familiar with, but I think the time has come to start thinking about catching up with the main repo.
This is just to open the conversation on how best to do this. I will soon start a new branch and try to prepare our branch for merging with this project.