Would it be possible for the baker to fire a low res bake, and then assign a lightmap resolution on a per polygon basis, with the resolution dependant on the difference between min and max rgb value?
For example, if there’s a big difference between min and max, this would indicate a lot of shadow/lighting detail on that polygon, so a higher lightmap resolution could be assigned.
A small gap would indicate less details in the shadows/lighting, so a lower resolution could be assigned.
If a per polygon option caused visible seams, then the user could swap to per object instead.