I just find out a cool feature,
it’s possible to instance a collection of collections :
I’ve got two air conditioners that I initially planned to merge as one object each to instance them. But in fact it’s possible to put each one in their own collection, all in a main collection that is used for instancing.
And from that you can do exactly as if they were regular objects inside a collection :
You can even set the center of each collection here :
The only thing that didn’t worked was that boolean cutter inside a collection seems to get treated as regular geometry: they’ll appear in the duplicate even if they are set to bounding box, I didn’t investigate further because I can totally live with it. I can keep the objects editable with most of their modifiers, without worrying about when to apply them. That make my day !