While I have no idea how that would be implemented, it does make me think back to Distance Field Indirect Shadows and the like. That was a per-mesh distance field, that could use interpolated GI from baked probes to cast accurate indirect shadows. I wonder if one could have a per-object surface cache parameterization as well, such that you could have a totally baked scene with only a handful of dynamic objects, and only need to pay the surface cache cost for a few of them.
All that said, Epic is clearly moving in the broad direction of entirely dynamic lighting, but the performance just isn’t there yet, at least not on consoles.