A wide range of complicating factors would limit the ability of surgeons to perform a cochlear transplant, some of which include:
1. The cochlear is also connect to the vestibular labyrinth, or balance organs. Damage to these could result in considerably worse symptoms relating to balance, including periods of vertigo (the kind where you'll be stuck in bed feeling naseous all day).
2. The cochlear contains the most metabolically active tissue in the body - the stria vascularis which is required for normal cochlear function. Loss of blood flow to this tissue for more than a few minutes results in irreversible damage, making transplantation difficult.
3. The inner ear and it's nerve are encased in bone --> difficult to access and difficult to replace + difficult to reconnect the wiring.
In summary --> at this stage, unfortunately, cochlear transplantation is a pipe-dream.
