I would love, love, love if I could self-host this and would happily pay a fee if it meant I got the source for the backend and could do that. Product looks great, but I will hold off until I find such an option.
I have been looking for years for a viable self-hosted Evernote/OneNote replacement I can sync between devices.
Takuya; You can differentiate from your competitors on business model!
If I may make a suggestion: I develop Joplin [0] a similar note-taking app, and it can sync with Nextcloud or WebDAV (some have made it works with the Nginx WebDAV module for instance), allowing you to control all your data.
It may or may not have all the features of Takuya's app though.
Why would you use CouchDB when flat files already maintain revision history in a Git repo? That is the advantage of Markdown and you've somehow made it more complicated than it should ever be. Google Drive also retains file revisions for you.
You could have a look at Standard Notes. It has a self-hosted version, Markdown support through a plugin, end to end encryption, and it syncs across devices. I use the "regular" service that syncs over their servers, but the self-hosted version should work, too.
I have been looking for years for a viable self-hosted Evernote/OneNote replacement I can sync between devices.
Takuya; You can differentiate from your competitors on business model!