I think, if they hope for rapid adoption, this library will be available for free (binary version) to download by anyone to make integration.
I don’t see any big news about someone integrating GI Works, which means people doesn’t give a ****. I’m sure if Epic would integrate GI Works into engine, NVIDIA would scream all around to announce big news about it ;).
But if the binary version of GI Works would be available for everyone… Well I guess there are enough people in UE4 community to jump on board and integrate it for everyone benefit.
Though it depend how much changes to rendering there is needed to maintain reasonable integration. If it can be non invasive and make use of existing systems, I think it’s more than reasonable to integrate it into main branch.
Note VXGI - GI Works.