@admin.register(Post)
class PostAdmin(DALFModelAdmin):
    list_filter = (
        ('author', DALFRelatedOnlyField),    # if author has a post!
        ('category', DALFRelatedFieldAjax),  # enable ajax completion for category field (FK)
        ('tags', DALFRelatedFieldAjax),      # enable ajax completion for tags field (M2M)
    )

@admin.register(Post)
class PostAdmin(DALFModelAdmin):
    # Perhaps an optional argument deciding if all relations should automatically be converted to autocomplete filters?
    # list_filters_are_autocomplete_list_filters = True  # should be default imo but I don't mind, I already have a base admin class
    list_filter = (
        'author',
        'category',
        'tags', 
    )

# some init file or some file that's imported during usage of this library

from django.db.models import OneToOneField, ForeignKey, ManyToManyField
from django.contrib.admin.filters import FieldListFilter

# functools.partial doesn't work because isinstance is a CPython function that doesn't take keyword arguments, *sigh*
type_checker = lambda klass: lambda item: isinstance(item, klass)

FieldListFilter.register(type_checker(OneToOneField), DALFRelatedOnlyField)
FieldListFilter.register(type_checker(ForeignKey), DALFRelatedFieldAjax)
FieldListFilter.register(type_checker(ManyToManyField), DALFRelatedFieldAjax)

# If you want to implement list_filters_are_autocomplete_list_filters the flag from the above example,
# I believe you should be able to wrap the second argument of FieldListFilter.register instead of just putting DALFRelatedOnlyField 

# For the below function to work you need list_filters_are_autocomplete_list_filters=default_boolean set in the DALFModelAdmin

def decide_filter_class(filter_class):
    # Django doesn't provide any better way to hook into this place for us to decide on a filter class easier if we want to 
    # tie it to a condition on the model_admin class
    def get_filter_class(field, request, lookup_params, model, model_admin, field_path):
        if model_admin.list_filters_are_autocomplete_list_filters:
            return filter_class
        for test, list_filter_class in FieldListFilter._field_list_filters:
            # If it equals and list_filters_are_autocomplete_list_filters we already returned above
            if test(field) and list_filter_class != filter_class: 
                return list_filter_class(field, request, params, model, model_admin, field_path=field_path)
    return get_filter_class
    
FieldListFilter.register(type_checker(OneToOneField), decide_filter_class(DALFRelatedOnlyField))
FieldListFilter.register(type_checker(ForeignKey), decide_filter_class(DALFRelatedFieldAjax))
FieldListFilter.register(type_checker(ManyToManyField), decide_filter_class(DALFRelatedFieldAjax))