Actually 0.3 to 0.4.1 is a major release with many changes including new mercurial versions and better git support with updated UI and celery for background tasks. If you see a new ssh feature is just added with documentation.

Kallithea is pretty easy to work with and extend. We recently updated and built a CI using buildbot. Rhodecode and Kallithea have diverged enough and are moving differently. Also its a Software freedom conservancy project so it will be supported, hopefully it can attract bit larger community.