it's not just that. Deaf culture is different from mainstream Anglo-American culture, in the same way that Latino culture or Quebecois culture is different from it. Deaf people have different experiences from what you do.
That said, I think this could be a great boon to people who are hard of hearing, rather than deaf. They've been raised in a speaking culture and it's not fair or reasonable to expect them to assimilate into Deaf culture without having, for instance, learned ASL.
Also, there's extensive cortical reorganization that goes on when you are Deaf - auditory centres get recruited into visual systems; visual systems get recruited into language systems. You're not just going to wind up finding someone who is Deaf (particularly congenitally so), giving them stem cells, and having them be able to hear normally again. At best it is going to take a long, long time, because the neural pathways haven't grown that way.
The best application of this kind of technology would be Hearing people who have lost their ability to do so.