#12607 proposed a new dango-model-with-dunder-unicode rule that flags any __unicode__ dunder method. We realized that this is already covered by PLW3201 (preview), but the error message could be improved to state that a dunder method is Python2 only explicitly.
The comments list a few dunder methods that were removed with python 3:
We should change PLW3201 to use a custom error message for any dunder method that was removed with Python 3.