I thought I’d tell here as well that I’ve started working on an importer add-on for Rhino 3d files (3dm). Much of the discussion for this script can be found also on the McNeel Discourse forum in the topic Using Rhino3dm in Blender . The add-on is currently written with Blender 2.80 in mind, I’m not doing an effort myself to support 2.79 - but help in that area is appreciated.
The repository for the add-on
import_3dm is public. Much of the code is still pretty early development, but even so getting geometry and materials in is possible, and works pretty well already.
edit 2018.12.12: released v0.0.2 as a zipped add-on. Remove the old import_3dm.py before installing - and update to rhino3dm.py 0.1.4.
You can check videos on my YouTube channel. Here some direct links to videos:
So if you use Rhino 3D as part of your workflow I hope this add-on already can help you streamline the process from Rhino to Blender.