Sure the PS4 will be able to Ray Trace. Just way worse than it will do Rasterization.
720p 30 fps Ray traced God of War 2 should be no problem.
Enemy Territory Quake Wars was rendered with four Tigerton quad-core CPUs (2.93 GHz) at 15 - 20 frame/s in 720p in 2008
The PS4 should be able to handle that at an acceptable frame rate.
In 720p at 30 fps PS4 could Ray Trace alot of older games. Maybe we will see some experimenting with Ray Tracing this Gen. Also some things are simpler and cheaper with Ray Tracing , we might see limited use in some games later in the life cycle. I guess that Hybrid Engines for Raytracing certain things might come this or next gen.
There are just things which are harder and costlier to achieve without Ray Tracing in the same quality. But broad use is still far away (10-20) years.
The further Graphics progress the more we will need Path-Ray Tracing and Voxels for the perfect graphics. It will come the time were its easier to simply Raytrace most of the stuff.
