I think the concept of non existing is relatively easy to understand.

If we used "storeroom" as an alias for the place where things don't exist, I'd personally find it more difficult to understand and find it more difficult to explain - especially as a lot of games may have a room called the storeroom. Certainly, I'll try to clean up the description in the documentation, but storeroom is not the appropriate name for the non existent place in my view.

I'm very sorry if it feels like you received too much disagreement for your well-intentioned idea . 

Language is very very tricky, especially when it comes to coding semantics and many people have many strong opinions.  Gareth (8bitag) will tell you how I struggled even to settle on the name of location (for game locations) rather than room. I went back and forward second guessing myself. Also a struggle was naming the entities section objects.  I thought it was just more ergonomic to non-coders but I can't escape that it's really wrong. But, it's done now. A design is a design and you have to stick to it.

The idea of having a location where objects are when they don't exist is sensible, and as Garry said, most adventure systems use this approach. In Adventuron, the name of the place where objects are if they are nowhere is "ether". I don't use it in the documentation as I don't want to confuse children or beginners by making it known that nowhere is actually somewhere. But nowhere is somewhere - and existence is a per-entity attribute that is altered when an object moves in and out of the ether.