Just so that no one misses this: I just now committed the new backend files to the 2.0 branch, so everyone can now install the 2.0 branch with the new backend included.
Remember you need to add the backend switch provided by Timbalu to your serendipity_config_local.inc.php after installing. Also remember that said installation should use 2k11 as the frontend template to make use of the new backend (since some files currently belong to 2k11's admin template, especially the CSS).
I guess this also means we'll be developing the backend within the 2.0 branch from now on, so I can safely delete my GitHub repository for the backend. (I really don't want to maintain two repos for this.)
YL