There are devices like this in use, i worked with automotive and we used a device like this to attach certified third party factory installed add-ons, they also translated vendor specific quirks in the protocol so that both sides would understand each other better. In essence the third party was kindof trusted but to be on the safe side we firewalled them to only allow a list of white listed commands, more like an API. Not having this kind of barrier for internet attached devices is inexcusable.