I think it would be good to at some point add .blend files support.
Blender has quietly become a standard part of the design pipeline. Has a huge community, also. A lot of teams now use it for concept modelling, geometry nodes and visualisation work, so the presentation-ready version of a project often lives in a .blend file. Right now that means exporting to glTF or DWG before sharing, which adds a step and creates a second file to keep in sync.
I think this does not need to be a perfect translation. Nobody expects shader nodes, modifier stacks, particles or Cycles-specific materials to survive a three.js viewer, and that is fine. Geometry, scene hierarchy, object names and basic materials would already cover the coordination and review use case, which is what people are sharing links for anyway.
The format is self-describing, so a .blend can be decoded straight in the browser and fed into three.js, at least for base geometry.
Docs: DNA - Blender Developer Documentation
Example repo with web viewer: GitHub - acweathersby/js.blend: Javascript Blender file parser · GitHub