Far be it from me to suggest that tech bros won't ruin a good thing, I really don't think these will have a subscription model because they probably won't have any kind of internet connectivity. They'll be like pacemakers, purpose built for a specific function (prevent tremors, reverse paralysis, etc) and designed to only do that function for as long as possible.
I'm sure there will be upgradable firmware at some point in the future but having your brain be connected to any kind of cloud service is the worst idea I've ever heard of.
$5k and then never use retinal scans for anything ever again to minimize the security concerns, sure.