Just my two cents 
You might need to wait on WebGPU to achieve the kind of mesh volumes you are talking about.
I think the state of WebGL right now is kool for less than 2000 meshes (Including InstancedMeshes)
But tens of thousands of meshes (Even instances) is way too heavy right now… But the WebGPU is the future and will be closer to the metal
Check it out: Web GPU - Babylon.js Documentation