With a fresh server installed, the default python that came with my stage3 was for python3 (the overall active python version) The scripts that come with subversion[extras] (like svn-hot-backup.py and mailer.py, and probably lots more in /usr/share/subversion/tools/..) were broken until I set my system python back to python2 (or alternatively you can edit the script and explicitly set it to run with python2). Not sure what the proper fix is, but it should probably work out of the box. Reproducible: Always
The ebuilds do RDEPEND on =dev-lang/python-2*.
fixed in subversion-1.7.6, should be on your local rsync mirror in a few hours