I feel like implants like this should require an open connectivity standard between the stimulator in the cochlea and the processor.

A friend has a bone anchored hearing aid, with an osteointegrated post. The two different companies that make BAHAs use different posts. Which requires more surgery if they want to change brands. It could trivially be made compatible and swappable instead.

There is no vendor lock-in quite like prosthetic vendor lock-in.

Trusting a company for 15 years to keep making a replacement product seems crazy.