It could very well be that Unity paid a hefty sum for the integration and that there is some sort of exclusivity deal attached to that but that’s all speculation and doesn’t lead anywhere. So Im not thinking that we will ever see an integration into the core of ue4 for all developers(Probably more likely that Epic will have it's own solution in a couple of years). For big companies that are using UE4 it's a no-brainer. If they need Gi, they just license it. What Im hoping for is a path for Indies to license it as well. A single indie developer is in no position to do that but epic could kind of represent indie developers of ue4. I agree that it’s very unlikely that this will happen but I had to ask 
And I`m not asking to get it for free which would of course be unfair towards larger developers that are paying for it. But a scaling model based on revenue or something along those lines could even make them some money in the end.