There has been work done toward re-working our current laws to fit observation without dark matter, but I think it just breaks way more stuff than it solves. The new model ends up being a worse fit for pretty much everything else but the galaxy rotation thing.

We already have weakly interacting particles like the neutrino, which don't interact with matter outside of the weak force, making them rather difficult to detect, it's not really that far out of the realm of possibility to have other particles that only interact via the gravitational force.