I’d like to add my voice to @alexander.potemkin here — I’d love to see a more robust backup option than basic iCloud. Two reasons:
One, I don’t see why I should trust Apple to not lose my data. I’ve used Apple products and services long enough to remember MobileMe/iTools and its instability. A backup stored in only one place is, while better than nothing, not something to count on. I understand that “most people are completely happy” with Apple’s promises, but that will change next time that iCloud has a catastrophic data loss or security breach.
Two, I find it valuable to go back in time and review how my notes have changed. This means something similar to git history would be invaluable to me.
A simple implementation that I would be satisfied with is some way to (1) do a full library export, and (2) automate doing the full export. Full library export comes up occasionally, see this question for example: Back up Info
It seems to me that a full-library Markdown export should be a simple feature to add: you already support per-project export, and a full export should be a matter of iterating across all projects and writing them to a target directory. Add a menu item, and done.
Export automation is trickier, but I’d be happy with a first version that just adds an AppleScript call that does a full-library MD export, and allows specifying a target directory. (From there, I can export to a local git repository and add the necessary scripting to do this hourly and push to a remote git repository I control.)
Overall, that seems like a great premium feature to add for data-safety conscious users with a technical bent. (I get that people like that are likely a small minority.) And I know how pretentious and pointy-haired manager that sounds, but it just doesn’t seem like it should be a ton of work to add this to the (excellent!) app you have here.