There is an alternative: you can use a MIME envelope to store notes. This way you’ll have a plaintext container and a way to attach files in a portable way.
Sure, I can do that. The problem is what to do if I want to mass update the metadata across an entire set of documents. It's just easier to do that with a DB.
I’ve built a note taking system based on this idea: https://github.com/knazarov/notes.sh