Surgical methods for CI are extremely damaging. Often you can lose remaining hair cells during CI implantation (the electrical stimulation bypasses this so you can still hear after).
There is an alternative surgical approach for delivering meds that starts at the apex called canalostomy. This has a risk to vestibular hair cells rather than hearing ones (but you only need one good vestibular ear to function after PT, ask me how I know
). As far as I know this hasn't yet been attempted on humans yet though.
Novartis had a hair cell drug that had to be infused directly into the cochlea since it was an AAV treatment. The surgery itself probably did more harm than good (it may have even damaged cells they were trying to transduce with the viral vectors) and their drug failed.
Companies like Akouous have drugs for genetic deafness and have an AAV platform. They described that they have their own unique surgical approach for this in one presentation awhile ago without actually describing the technique. If that's true, they may have the surgical answer for direct drug infusion since AAV drugs depend on it. I'm following them to see how they progress.