This is really interesting. At first glance, I was tempted to say "why not just use sqlite with JSON fields as the transfer format?" But everything about that would be heavier-weight in every possible way - and if I'm reading things right, this handles nested data that might itself be massive. This is really elegant.

My one eyebrow raise is - is there no binary format specification? https://github.com/creationix/rx/blob/main/rx.ts#L1109 is pretty well commented, but you can't call it a JSON alternative without having some kind of equivalent to https://www.json.org/ in all its flowchart glory!