Here is a quick test using the export of instance matrix to a scatter file as I mentioned in the blender plugin section.
The workflow is a bit tricky but all in all it can be usable, the main goal was to see how Octane manages such high volumes, I find the rendering a bit slow but still ok.
The scene uses about 1.1 Gb of VRAM and has about 5.5 milion polys with instanced objects
Instanced object :
Grass generated from particles, about 2.2 milion faces
5 Different trees scattered based on Blender instances, only the parent object (trunc) is duplicated in Blender and is used as proxy
If I find some time I will test with another scene with some heavy forest on background, the Greenhouse scene could be great to populate with lot of plants and trees ...
