Just to clear up confusion for people who stumble on this thread.
No part of Joplin is proprietary. I understand that it's frustrating for users that Joplin stores data in non-transparent way (database vs. flat files). But proprietary has a specific and legal definition that does not apply to any part of Joplin.
In Joplin you (the user) have complete ownership of your data, but the application is the sole manager of that data (with the exception of technical users who understand the risks of messing with the database).
This is not the same as being proprietary because the format Joplin uses is open, it's an SQLite (open source) database, with a published schema. Any user is free to open and explore the database with their favorite database tool. Another notes project could even copy the database schema and use it for themselves, which would actually be really cool.
That said I understand the desire to have the option for full user control and I am sympathetic. My only intention in writing this is to clear up that misunderstanding and prevent the inevitable criticisms about Joplin being proprietary that use your post as evidence.
Edit: You might be interested in this static site generator export plugin .