Is it possible to list a scene’s contents without opening it from an editor script? In a similar way to how importing a package works, I would like to list a scene’s contents before having the editor script open it.
No, you can’t. However you could force a save of the current scene (or ask the user), open the scene, get the list of content and reopen the previous scene. AFAIK that’s the only “safe” way.
I would love a feature to load a scene into a GameObject in the current scene. That would be quite handy for content swapping and dynamic level loading.