The way it appears to be working is that some polygons are being rendered using Raytracing rather than fragment shaders. So it's not a complete overhaul of the graphics pipeline like I expected. It's basically just a post processing step now and can be added like any other post processing effect. Which means it can be bolted on to an existing engine pretty easily.
That being said I would not expect it to come to many, if any, existing games because there's no profit incentive to do that.
And don't fall for the hype. Rasterization is almost as good as raytracing 99% of the time and runs significantly faster.