What problem does this solve or what need does it fill?

Ability to use Scene as a prefab, in the sense given by Unity: one-way irreversible spawning of a group of entities and components.

What solution would you like?

No SceneBundle, no SceneInstance, no SceenSpawner. Just a way to spawn the content of a scene anywhere (including at the World root, without a common parent entity, so ability to spawn multiple top-level entities as a flat list) and forget forever that this ever was a Scene.

What alternative(s) have you considered?

• SceneBundle. This has all the mentioned extra "features" which are just getting in the way most of the time for typical "use a prefab to spawn multiple things" usage. This is also missing some features like spawning without a single comment parent entity.
• Spawning function. This only works if you hardcode the collection of entities and components, and is hard to work with (spawning via code is tedious).

Additional context

Possibly related to #3877, #10907