For example, semanage dontaudit -l fails. Everything works fine if python 2.7 is used as default. This used to work before; have you perhaps removed some code from the ebuilds which used to hardcode python2.7 in the shebangs?
Can you try out 2.6? All the python3 stuff should be in there. It also uses setools4 which completely supports python3 too.
After upgrading to libse*-2.6, policycoreutils-2.6 and setools-4, everything works fine again.
2.6 is stable