Do the possibilities include the matter being converted to massless particles such as photons? Or perhaps that the energy is stored in a field with no particles at all? Perhaps other types of conservation (charge?, baryon number? ...) forbids those scenarios.It certainly seems likely that whatever is there is broken down into elementary particles but we don't know that and likely won't until there evolves a provable theory of quantum gravity that may (or may not) let us figure out what is likely to be happening at the quantum level.
It always seemed to me that science should discuss the energy inside the BH based on the observation that it gravitates, and avoid any presumption about the form of that energy since we don't know for sure.