Little over a week ago I published a programming language called plang (as in pseudo language).

It does exactly what you are describing in this post, all data is local, has identity (so no passwords), data is encrypted on local device but with ability to sync between devices securely.

Another benefit it has is that the code is verifiable, the app you create is just series of JSON files that anybody can read, do verifiable.

Yet another benefit is that the code is written in natural language, making it easy to understand what is suppose to happen. I call it intent programming. You can see more about it at plang.is