I really wish they would 
I was originally optimistic when GPU lightmass was announced and Epic had said Lumen reflections would support lightmapped GI. But I didn’t realize lightmapped GI support for Lumen reflections would just be a hardware raytracing option, and GPU lightmass has really languished since the release of UE5.
Just to clarify I don’t think that Lumen + Lightmapped GI only sampling the VLM is intended. I’m certain that at one point, it DID sample surface lightmaps correctly, but I guess at some point it broke.
As for how it would work with software raytracing my thought was that it would use distance fields and surface cache, the same way Lumen reflections currently work with Lumen GI. Except the surface cache could be pre-computed for the static lighting. I don’t know how performant this would be in practice, it might not be worth it.
Slightly Off Topic
At the risk of getting too off topic there might be better options. For example Mafia 3 stored depth in their reflection captures and traced multiple sets of them to get the hit result. It covered the entire roughness range and ran on a PS4 at 1080p in 3ms. The results were remarkably good quality imo, even if it did have some… weirdness on mirror surfaces.
Frostbite also somehow implemented approximate specular from their lightmaps without the need for any reflection captures which has some downsides (that he explains) but still looks really good.
Unreal’s static lighting was built for UE4 and iirc it was intended for the xbox 360… On modern hardware I’m sure if it were a priority the team at Epic would come up with something great. But since Fortnite doesn’t need it… well… I suspect it won’t be a priority.