Arguments for feasibility:
Hearing aids are positioned to put a microphone as close to the eardrum as anything I can think of.
Hearing aids already have ample power to cancel out ambient sound. I think of it like this: We hearing aid users cannot (to a greater or lesser degree) hear the ambient sound that reaches our eardrums, at least not well enough to fully understand it. But our hearing aids have the power to amplify the sound enough so we can hear and make use of it.