It's kind of an interesting premise I suppose. I have hard time believing there wouldn't be some non-networked part of the technology that could shut down the implants in the event of a "health" emergency and automatically contact a hospital.
I'm sure if such a technology existed, there would be people who have adverse side effects that aren't detected until after implantation. I'm imagining like epilepsy for TV or games these days as something to compare to. Imagine the rustled jimmies and law suits. It'd pretty much necessitate a back up safe guard of some sort.
It's true that's nothing is 100% secure, but you can prevent all out attacks like that. No need to straw man this.
I think the more interesting thing about this series is it's being made by Warner Brothers. Are they trying out a new content delivery / revenue generation model or are they simple testing out the series concept for possible future development?