While it depends a lot on the implementation I think Pascal's 1.5x to 3x hit in games so far from enabling DXR means it's still kinda useless below a 1080Ti besides demonstrating to people why they didn't open it up originally, at least until games start implementing lighter and lighter DXR implementations which to be fair should come as the tech matures and people work out where the "bang for buck" lies in terms of visual impact vs performance impact, but then that will also come alongside making somewhat better use of the high resource raytracing elements so there will presumably still be a pretty clear gap in the type and amount of effects that are capable on accelerated hardware.
I think this also makes it pretty likely AMD went the route of making their shaders better at the compute workloads used in these semi-software based DXR layers as opposed to creating dedicated execution units for it, really they had to wait until the tech matured somewhat and lighter implementations started to come until that was a viable route(And I wouldn't be mega surprised if Navi launched with these features coming later in a driver update, Radeon VII now has reasonably well accelerated DXR fallback layer support but its clear work still needs to be done on the software side).