I would find it really useful to be able to create Ghost Categories within my Stores pointing to Categories in my other Stores.
An example where this would be beneficial: I have recently opened a new store selling Postcards. However I also have transport postcards in my “Buses Galore”, “Trams Galore” and “Railway Relics” stores. I would much prefer to have all these postcards in my Postcard store with Ghost Categories pointing to them from my Buses Galore”, “Trams Galore” and “Railway Relics” stores.