I want them hackable by me and hardened to anyone else.

When an article such as this mentions hacking, they don't mean your version of hacking. They mean the spooky news definition of hacking where there's a stock photo of a guy wearing a hoodie (and a balaclava for some reason??) typing on a laptop with a glowing green matrix waterfall on the screen. They mean there's no precaution taken whatsoever against malicious access, which is certainly a bad thing. Even the most radical FOSS guy who built his own phone out of spare parts and has a bumper sticker which reads "my other computer is your computer" is going to put a password on it.

There are pacemakers out there using NFC or some similar tech to talk to an external processor and battery pack. I bet the security on those is utterly tragic. The relevant regulatory bodies are absolutely not going to do a damn thing about it until there's a body count--of that much I am 100% certain.

Murder via medical device malware sounds like the plot of a rejected Gibsonian short story, but stuff like that will happen in our world. Somebody is eventually going to think that might be just the way to off grandpa so they can hurry up and get that inheritance.

Could there be a key model where you could unlock access and then control via chosen (hopefully reliable) software?