How can black hole interior theories be falsified? How can any theory of the interior of black holes be falsified if the interior cannot be observed?
 A: A theory that describe the black hole interior is intended to give some predictions that is testable even outside the horizon. For instance the internal "dynamics" could be relevant to tell what is the final state of the hole after the evaporation and what are, if there are, the correlation in the Hawking radiation. 
If the putative theory gives the right results, then one can say that the theory is correct, even though it's non testable inside the hole. Just think that one of the greatest theories of all time, Quantum Field Theory, talks about virtual particles, that cannot be seen even in principle, but that gives the right results after loop calculations. The same for many blind spot of quantum mechanics. 
Anyway there is another possibility. Maybe you have heard about the fuzzball proposal in string theory. The idea is that basically classical black holes don't exist! Horizons are classical approximations, like the point-like shape of particles in classical mechanics. The hole is more similar to a star that to a traditional hole.
With some collaborators we are working to construct fuzzball solutions in 4d that can account for the entropy of the black hole, that are smooth and free of any singularities (both on the putative horizon and inside the hole). We have already found a supergravity solutions that account for the microstates of the hole and match holographically with the microscopic D-brane states in string theory. I put a link to the paper, even though is technical. 
Another interesting approach is the ER=EPR, in which basically quantum entanglement is related to wormholes going from the interior of the hole to the exterior.
Paper on 4d Microstates 
