Hi! Thanks for your comment and this is a very interesting question. I tried with 1 million grass scattered in a flat surface to test performance (I will upload a video later) and it works just fine in my laptop. Regarding multimesh instance, it’s a single object, and it gets culled out when you are very far away.
I made NatureBlocks with the idea in mind that you need to be building worlds not in a whole big one piece but smaller manageable chunks stitched together. So each mesh will contain the grass multimesh node, and as Godot does not render what’s behind the camera by default, this will save you a lot of performance. So it’s more like a terrain set-piece with grass/ shurbs and other assets on it, then you spawn them on your scene throughout.