Earlier quoted context omitted.
That's exactly what I just built for myself. Flatnote, on the windows store (and soon on mac/Linux/mobile) is a rich-edit note app which stores files as .md files in the file system. Sync is handled by just putting your notes folder in Dropbox
That's interesting, I've tried to use plain text files at the beginning too but it didn't quite work. Also if I'm not mistaken on mobile Dropbox sync is not built-in so you'll need to implement it on top of their API (including conflict handling) which is probably the most difficult part in any app like this. That's also why having a local SQLite is useful because you can more easily compare your local state to what…
I do have a local database store, but the Windows Store app is written in JS so I'm using NeDB which is basically just a mongo style interface for a JSON file. At the moment I really only use it to track recently opened files.
On other platforms I'll probably use SQLite, but I won't be storing the data in there, just the metadata (access times, paths, previews, wordcounts etc)
As one dev to another I have to say I love what you've built in Joplin. I love the name, I love the terminal app idea (Why didn't I think of that!) - its really a great achievement. You've built for multiple platforms and here I am hijacking the thread to peddle my half-built markdown-editor-with-a-file-list =D