I did some interesting things with folders full of GeoJSON files. It seemed fortunate enough that GeoJSON is a well supported lowest-common denominator for a lot of tools (esp. web tools) and if a thing didn't take GeoJSON there was some simple middle tool (usually a quick Python script). Pretty-printed GeoJSON gives you okay-ish diffs and if you go to an extreme like single feature per GeoJSON file (like I said, folder full of GeoJSON) and have other tools (often Python scripts) to reconstruct/deconstruct layers from all the separate files, you get things like commits/PRs where you know at a glance exactly which features changed (from the file list).

Certainly a lot more work than this new project, but as the old saying goes I suppose you should never underestimate the database power of a folder full of files.