[nine_k]

Since OpenSCAD uses basically source code format, it already does.

I'm more interested in tracking and versioning edits to KiCAD schematics, for instance.

[bgnn]

I think you are describing something similar to Perforce Versic [1]. I use this at work to diff schematic or layout. The ugly thing is: it's perforce.. I wish there was an open source alternative.

[1] https://www.perforce.com/products/versic

[fanf2]

KiCAD’s storage format is s-expressions, so it works OK with git (better than binary file formats). However I have not tried to merge concurrent edits by multiple people; I suspect if there is any conflict you are basically out of luck.