Or it might be time to start looking at other things entirely. Especially seeing as there has already been a considerable amount of work on finding 5th forces both attractive and repulsive When new theories start contradicting experimental data or start making statements that are untestable, at some point you have to drop back and say you have been barking up the wrong tree.
I'm not sure what you're getting at. Science follows a simple recipe: observe, predict, test. We observe that galaxies rotate in a manner that cannot be accounted for by our existing understanding of gravity and matter. A whole bunch of predictions have been made according to different ideas about how to account for galactic dynamics, from gas clouds to black holes to brown dwarfs to modified gravity to exotic particles. From time to time somebody comes up with a new idea to add to the list. Those predictions are being tested and eliminated, and so far the one that's holding up best involves exotic particles. You can be sure the more prosaic possibilities were studied first, but it turns out they have not done a good job in matching observations. But it will take time any many experiments to uncover the truth. Meanwhile we will continue to bark up all the trees that are still standing, and search for new ones to climb.