The optional features (Polymorphic and Django filter) should define their dependencies as extra.

Currently this is only done as test requires but actual users won't have enforced minimum requirements.

Once this is done a user can simply add following into their requirements to properly activate an optional feature:

djangorestframework-jsonapi[django-filter] == 2.8.0

see
https://setuptools.readthedocs.io/en/latest/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies