I'm no expert, but there are many papers from 10 years ago where they identified a signaling gene whose concentration was not being raised enough for the neighboring cell to divide and replace the hair cell, and it was claimed that in 10 years hearing loss would have a cure. We seem to be more or less at the same point though, because it is not clear what goes wrong in the signaling pathway, or whether if that is the only issue. IMO too little is known to answer your questions.
