Another version of this idea that's been around for a while is CherryTree. I would use it a lot more, but there's not really a way to use your notebook on mobile due to it using a special database format that nobody cares about. I love the idea of this program's data instead being a regular folder of regular plaintext files that you can do anything with. In a perfect world everything would be like this, where your files are just your files, and client programs just help you use those files in more effective ways.