Any objection to removing those models from documentation in 1.8 and 1.9 and removing the models themselves in 1.10? (Actually, the models would be moved into the test suite instead of shipped in django/contrib/auth/tests/custom_user.py -- this is done in [2].)
[1] https://code.djangoproject.com/ticket/26089
[2] https://github.com/django/django/pull/5975