Assorted challenges/considerations for scene composition

[ecoskey]

(Non-exhaustive)

1. what patterns do we expect to see sub-scenes used for?
2. do we expect to need multi-scene editing in the same viewport? (the only reason I can see for this is loading/unloading scenes dynamically at runtime, where you couldn't have them as sub-scenes themselves)
3. when editing a sub-scene, how to display native entities vs overrides (for components as well)
4. how to choose editing the original sub-scene vs specifying an override (could we even handle this for depth >2?)
5. which scene file to add new entities to?
6. if we support dragging assets (such as scenes) into the viewport to load them, which scene will they be parented to?
7. how to differentiate objects from different scenes/sub-scenes? (colored highlights, accents?)
8. how do we handle scene selection so that we don't clutter the viewport with multiple scenes at once and don't have multi-scene editors annoyed that their extra scenes keep closing?

[ecoskey]

Terminology: sub-scenes are the bsn equivalent of prefabs from other game engines, with similar(but not the same) considerations. Specifically they’re bsn includes (from what I can tell from the proposal)