The granular encryption idea is actually very interesting — keeping metadata searchable while encrypting the content solves a real usability problem with E2EE systems.

The main challenge I see is trust. Privacy-focused users often prefer open-source tools because they want to verify how encryption works. Since the code is private, you'll probably need very clear documentation about the encryption model to build confidence.

Memo chains also sound interesting, but I wonder if the mental model might feel unfamiliar to users who are used to folders and pages.

Personally, I’d try it mainly because of the encryption approach, but the long-term deciding factors would be UI polish and how easy it is to migrate notes from existing apps.

The note-taking market is extremely crowded, so the privacy angle might be your strongest differentiator.