This is just remotely interesting for Blender people, I just hope you find it interesting.
I just released v0.1.0-alpha of my rendering engine, Gonzales:
I just works on the CPU (for now) but is able to render big scenes, e.g. it now renders Disney’s Moana in 78 minutes, thanks to Embree.
Thanks for reading,
Andreas
Very interesting take with the Swift language. I think that there are great chances now for some new sort of programming, where more creative ideas can be explored.
Though without underestimating the nature of C++, I have looked at various codebases (even from nVidia) and I might say that, implementations are always bulky and play safe.
The benefits from going to the route of a different language, is to look at the problem from a different perspective.
This may be so… But sometimes it is also just reinventing the wheel… i mean what’s important is the mathematical modelling of physical light properties… and not the language in what it is written in… so if pbr-book.org was an inspiration… then it is following the same re-search done it this book… and this implementation may also be more dicussed… 
…just my (unimportant) two cent…