As far as I know there is no way to do this yet. If they are offering us a node to get a random number seeded by the instance index, I don’t see why we shouldn’t be able to access the instance index directly. It is stored on the gpu, right? Wouldn’t need to be additional draw calls? But the node isn’t there.
Depending on your use case, you could maybe hack something out using worldPosition, and using only it’s x,y components so you know where you are in a plane.
If your instances possible positions can be divided into a grid, and that grid’s measures are known, then you could know if your world position is in a given repetition of that distance, so in a given grid number.