Unfortunately I think from what I have read that this is impossible/ performance prohibitive for the foreseeable future.
In the inside unreal video about valley of the ancients they talk about how they had to make assemblies to optimise and limit the amount of overlapping mesh instances because the way nanite decides what poly’s to draw or not gets bogged down with too much overlapping.
If you do this to a field of grass or leaves, and throw opacity into the mix as well then it would be more expensive then the current method.