Would it be possible to bake each object to it’s own exr and 1:1 tile, and then combine them all into X number of uv tiles/bake.png’s only during upload/packaging/or running locally outside of the editor?
So a seperate editor folder for lightmaps for each object which the editor would use, and another folder which contains one lightmap containing the result of packaging all the individual lightmaps into one tile, along with the accompanying re-packaged uv’s.
This could mean that whilst still editing, individual objects could be re-baked instead of the full scene. Handy if for example you need to change the lighhtmap resolution of an individual object, or even if you just want to import one new object and bake it on its own.
I was going to say use the final packaged uv’s but render out to individual EXR’s, but this would mean new objects couldnt be added without re-baking everything, because the uv’s would need to change to make space.