So now every program that interacts with the registry in that way needs to implement transactional IO operations correctly and sanely, and if they don't bad thi

So now every program that interacts with the registry in that way needs to implement transactional IO operations correctly and sanely, and if they don't bad things will happen? A thing that is so complex Microsoft is considering deprecating it due to that alone? You also didn't mention concurrent access, or think about random code writing random completely invalid data into files, or consider how you would evolve the on disk format. That sounds awful burdensome for a simple key-value api. Perhaps you could use some kind of service to shield clients from that complexity, and so you don't have one dumb program messing the entire registry up for everyone else. That would be cool. You could call it the registry service.