Epic is well aware of GPU rendering as an option for lighmass, but there’s some likely issues
- Epic would have to re-write lightmass from scratch.
- Results might not be as high quality (people already complain a lot about lightmass and seams).
- You probably couldn’t work in the editor while baking using the GPU.
- The editor/GPU lightmass wouldn’t scale well for lower end machines.
They might get around to it eventually, but if reasonable settings you can get a decent lighmass bake pretty quick. The Lightroom: Interior Day Light by Koola example scene bakes in about 5 minutes for me.