Hi there, I have the exact same problem. As soon as I turn on Raytraced mode it crashes, even without any objects/model… The cycles render device is set to CPU.
For some reason, it is impossible to switch to render device GPU/cuda, despite having an Nvidia GTX 980 running well on other applications…
Any clues yet? Would be great having access to the new Cycles Ray Tracer…
Nvidia cards are useless in a Mac these days, due to Apple & Nvidia not playing nicely which affects 1000’s of users with these cards in them, afaik there are no up to date drivers and it doesn’t look like there ever will be. Saying that you should still be able to use Raytraced mode with CPU set. @nathanletwory is probably your man to assist with this issue 
I believe this is a Rhino bug that hasn’t been fully pinned down yet, because I’m using a Radeon Pro 460, and Rhino also crashes from time to time, when switching between the raytraced and another views. Since Rhino for Mac doesn’t produce crash logs most of the time, the bug is hard to catch! It might be wise to fix the crash reporting first, if at all possible.
Yes more or less, that is a sad story the Apple/Nvidia thing. But this particular Mac Pro works very well in other software, as we have the appropriate Nvidia drivers and Mac OS. I would at least have expected no crashes when using Raytraced with CPU.
I still don’t get consistent results in Raytraced using Rhino Mac, I haven’t given up rendering in Rhino but tend to take my model into other software to render out, hopefully Rhino will mature on the rendering front as times goes by. It doesn’t crash on me though, but it does crash if I use ViewCaptureToFile in Raytraced, I’ve never gotten that to work. My machine is now 5+ years old and getting a bit tired when asked to perform certain tasks 
Yes, the new rendering capabilities/cycles with material system seems impressive on paper and was part of the reason we went with Rhino version 6, for a more complete package. So I would expect it to work properly further down the line… Even if a machine is a bit “tired”, in my book the software should not crash, as long as it corresponds to system requirements.
FWIW, let me state again that I am getting the crash in a release build as well, but haven’t this one in debug yet. This is rather crucial if I am to do an actual fix. Until then I’ll have to guess and try something.
I’m regularly trying to reproduce it in my development environment. If I get this fixed you all will hear about it.