But the most power comes from presets and getting used to just using the presets as game objects from a tool box. This way if you add a door then add a switch you will only need to tell the switches property what door to open. All switches are defined (hypothetically) to open the chosen door.
Think of anything you add to scene as a game object either dynamic, static or fully optimised. All communicating with any active game system. Want a building, drag to scene now you have a building with physics and any other add-ons it has, can even be many models as a single preset. Want to drive past the building get a car, press play and you drive. etc etc
I see this brings problems with models, as you add a model you don't want to then have to make a preset and save it to another folder

Q) Now if we were to create this new active library what categories would be good?
Heres my current idea: