In fact I’m pretty sure this behaviour dates back to NSOpenGLView and possibly others. I suppose technically this has always been the case; that overlapping views weren’t supported at all before layer-backing. But I had forgotten, so it took a little bit of experimenting to jog my memory.
It’s interesting that when not layer-backed, all that happens is that the SCNView draws over any overlapping views. If its background colour is transparent you can actually see the views overlapping it. In any case, they can receive events just fine.
Tangentially, that you can use translucency to reveal other views “underneath” your SCNView is interesting. You could use it to present a relatively fixed backdrop for your 3D world, for example, rather than having to deal with actual SCNNodes and camera movement and all that.