I read this article, I think comprehensive hearing regeneration is way too complicated and I wonder if it will occur anytime soon at all. I think it'll take the better part of a century.Don't know if someone already posted that link (published 2012).
Good explanation about severe/profound hearing loss in the cochlea concerning epithelium condition.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637947/
On one hand it says that severe to profound hearing loss patients are potential candidates for hair cell regeneration on the other hand things like Atoh1 didnt work in such damaged areas but I dont know much about Atoh1 so I cant comment on this anyway....
Maybe limited, partial regeneration will be a reality soon(er).