By and large, implantable devices are for more extreme hearing losses or unusual conditions, and I would expect very few people who get by with a HA to switch to an implantable before it's necessary.

Especially since the hardware is not upgradeable without another surgery, assuming it's upgradeable at all.

If you have HAs and wait, 1) the implant tech may get better, or 2) medical science may be able to regenerate inner ear hair cells. For #2 in particular, cochlear implants may prevent that from even being an option, since iiuc, they damage the cochlea.