I realize that what I'm asking for is something that, by nature, converges on a re-implementation of the
.blend file format (or a GLTF-style exporter that precisely mirrors
.blend) as it gets closer to full functionality.
I also know we could write our own. Traverse the hierarchy, extend
JSONEncoder, etc. Some good work has also been done recently on specifically serializing materials, and there's a couple questions about writing exporters, but I haven't found any that (1) aim to work on entire object hierarchies (including geometry data, modifiers, relationships, etc) and (2) fully preserve the data and structure for continued use in Blender.
I wonder whether any other work or tools are already out there.