Maybe I'm missing something, but this doesn't look like path tracing to me. The comparison shots just look like the same exact lighting system, but brighter. I found myself actually preferring some of the "before" sides, to be honest.
It can't use path tracing because many of the light sources in Skyrim are fake (unless they require another mod that fixes that). Many things that look like light sources (torches, windows, fireplaces etc.) are not, and there are hidden light sources sprinkled by developers instead all over the place. Occasionaly they happen to coincide but it's the exception rather than the norm.
Lighting in Skyrim in general is a mess and there are many mods dedicated to fixing the original lights, shadows, ambient lighting, sun & moon etc. If anybody's interested read through the descriptions for mods like Relighting Skyrim or Realistic Lighting Overhaul to get an idea.
I've had countless times where I've modded skyrim to "perfection", had it exactly how I want visually, then I enter a building and get the overlapping light sources bug. In the end I find it impossible to fix, impossible to tolerate, and my gaming experience stops there, I've never actually finished skyrim I just always go through this cycle.
Marty's mod uses the fake light sources to convert into path traced sources. This is SS level change and not something done in engine. Think of how ENB or Reshade works. This is a plugin for Reahade. Your lighting mods will still work (and will still be recommended)
Community Shaders is also working on doing a complete swap of SSEs lighting system at the engine level that will not suffer from the massive bugs CE has and will be much more performance friendly than ENB Lights.
Maybe they didn’t choose the best comparison shots, but the technical details of what’s happening with this mod is really interesting. With his mod, it’s approximating global illumination in world space vs the standard screen space methods, so it’s accounting for bounced lighting from areas offscreen.
The cool thing about it is it’s implemented via Reshade, so you don’t need a ray-tracing card to make it work as far as I can tell, and it should be compatible with games that RTX remix won’t be able to touch.