I mean ray tracing is (probably? I'm no expert) the most physically accurate rendering method available, mapping closely to how light works in real life ('rays' of light bouncing around until they hit your retina, but then in reverse so you only simulate the rays that actually hit the camera instead of wasting every one that doesn't). But it's also the most expensive one.
We're at the point where we need new systems to represent material surfaces better, like leaves glowing from beneath when sun hits them from above, since they're thin enough for light get through. Or imagine putting a flashlight on your skin and seeing your skin glow from the inside around it. Unfortunately a much more complicated scenario than large open rooms and solid flat walls.
Games do simulate subsurface scattering, it's been a staple since the PS4 generation. They currently fake it rather than brute forcing the light paths traveling inside the surface like offline renderers do, but it still works fairly well.
In offline rendering the sky is the limit when it comes to SSS quality, if you have enough compute to throw at it. It's essential for getting skin to look right.
They don't understand or are not aware of the existing systems. UE for example has had a "two-sided" foliage shader model with normal mapping and subsurface scattering for ages.
Ray tracing algorithms are quite simple - it’s essentially just checking line intersections with geometry and doing bounce calculations - but a VAST number of rays are needed and a GPU that can do ray tracing needs to keep much more information about the scene geometry in memory. In older generations you wouldn’t store detailed collision information in GPU memory.
A GPU that can handle ray tracing, however, can do a lot of the techniques mentioned in the article (and others) more efficiently without doing what you’d consider full scene ray tracing, because the fundamental path tracing algorithms are very versatile.
Sorta, in classical single-bounce ray tracing you still need to cast explicit shadow rays from diffuse surfaces. Path tracing gives shadows for free, because it is simulating global illumination rit large: ambient occlusion, shadows, bounce light are all special cases.
In traditional Whitted-style ray tracing, the expensive part is indeed figuring out where there is no light. You know where you are, you know where the light is, but is there something inbetween?
