Troubled Times for Alternatives to Einstein’s Theory of Gravity
I still think the answer will have to confront the problem of local realism.  It was the issue that drove Newton nuts (that gravitation was, in Einstein's language "spooky action at a distance"), and Einstein resolved that through Relativity, which redefined how we think about "distance".  Now the lack of local realism in QM is driving Einstein's ghost nuts.  I think the resolution of all this will again redefine "distance" to take resolutions involving quantum entanglement into account.  Vaguely I picture some quantum relativity theory where from the perspective of an entangled particle it's still d=0 from its entangled partner and everything else is splitting apart.  So like relativity, it's all about which perspective you take.  Then perhaps with these relative distances, and however the math falls out with some kind of quantum Lorentz transforms maybe we see that in galaxies with lots of entangled particles this can slow down rotation.That said, dark matter is entirely possible too.  There's no particular reason to think that all particles need to have an EM effect as well.  In fact it's somewhat crazy to think they should.  Why wouldn't there be particles that only show themselves gravitationally?  Or through other perhaps insanely strong forces that for whatever evolutionary reason Earth Life is just not evolved to care about or see even indirectly.That said, I have no training in physics and this is entirely crackpot concept.  (Of http://www.goodtheorist.science/ I've only read ~6.)