Yes, it is a key/value store as base technology. The important thing is that you can build anything you want on top, which includes for example indexes and such. The idea is that this can/will be implemented on top of a simple base protocol, which is easy to implement, and to use data modules (and shared utility modules) to add more complex functionality.

However, having used RS apps for years now, I think it's worth mentioning that most people considerably over-estimate the amount and size of the personal data they use daily, and in the case of notes, I never had performance issues with Litewrite pulling all my notes whenever/wherever I connect my storage: https://litewrite.net/

That's not just because this is actually pretty fast with multiplexing on HTTP/2, but also because you usually don't connect and disconnect all the time on all your devices. So you will usually have your existing data cached and available on app startup (including when you're offline), and only sync remote changes when you get online. This is also what similar proprietary apps like e.g. Google Keep do.