Got a lot closer with the shadowOnlyMaterial… Occlusion of objects AND shadows on the surface. I switch over to it at 1:06 into the video, after mapping is done.
I completely forgot that material existed, but it is well suited. Amazing how reliant (and how flexible) the Standard Material and PBR materials are, you tend to forget about all the other amazing options we have 
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Now if only it would catch reflections, and allowed for more than one lightsource it would be perfect.
May have to build something custom in the future as this seems like a super useful material for any sort of AR work to blend objects in the scene without tricks like shadow catching meshes attached to the base of models (UE, Unity, all do this approach). Currently don’t know if I am up for the challenge of that one though.Thoughts on how to go about doing this would be appreciated.
Edit:
Hmm, looks like @Evgeni_Popov may have been working on a simular challenge a few years ago… Custom transparent ground that receives shadows, show mirror and use diffuseTexture - #18 by Evgeni_Popov