Adress nested collections via Geometry Nodes

It could be quite essential to navigate down the hierarchy of collections using Geometry nodes.

Example: a procedural building is made up of 25 different collections with parts (roofs, corners etc.). Now the user wants to change the building style. He'd need to change 25 collections to reference the other style. It would be easier if one could just select a single "master collection" and the subcollections could be sorted out using nodes.

You wouldn't want to put all parts in one collection, because then you could not vary the number of part-variations per collection without breaking the node setup - so nesting collections is unavoidable.

However, right now all subcollections are joined into a single object, after one separation.