Mammals are the only animal class that can't heal damaged hearing. The gene thought responsible for this has been identified, so there may come a point in time when the CRISPER molecule's work can be better controlled and when we might be able to alter that gene and start healing our hearing. Unnatural, evolutionarily speaking, but possible. If the beneficiaries of this treatment then go on to grow gills afterward, I may be concerned. In the meanwhile, expect any such treatment to become available for pets before it is for people.
Additionally, in the last year or so, someone succeeded in deafening mice and then recovered their hearing by placing stem cells in their inner ears. That's a treatment that may come around sooner than the gene splicing.
It's a brave new world.