I own quite some CAD and 3D Apps, so far unfortunately none has Speckle Support - besides Blender, which I was not very experienced with.
So now that I learned Blender a bit and am more familiar with it, it was time to try at least a Blender up and down stream, to finally see what Speckle is really capable of.
And I have to say I was positively surprised and quite amazed 
Thank you very much Speckle !
I get Materials and Cameras in, even with proper Naming. Geometry looks totally OK, and Collection Hierarchy. This helps a lot.
I found a few issues and realized it works best with a better with latest Blender-Standard, well organized Blender Files. So I did some File optimization and finally got a better stream.
I will open another Thread with my findings.