It's all about make "variant scenes" ("prefabs") from other scenes.

[sttifer]

Describe the project you are working on

A new Tiny Action RPG

Describe the problem or limitation you are having in your project

It's all about make "variant scenes" ("prefabs") from other scenes.
Real example:
I made a scene called "Object" (it's simple, has KinematicBody2D node, and a Sprite child node), and, of course, i saved.

Now i needed to make a new scene, for example, "Key Object", but this scene is exactly same as Object, but need to change the Texture in Sprite node. What did I do? I instantiated a scene "Object" and i activated "Editable Children" and change the Texture. Perfect! Almost ... When i saved as ".tscn" ("Save Branch as Scene"), i got the message: "This operation can't be done on instanced scenes".

But why? I just want a "Variant" of this scene. I don't want to "make local" before "Save Branch as Scene", becouse if i change the scene "Object" i want to change .all derived scenes.
I think make a ".tscn" ("Save Branch as Scene") from a instance would help most of designers to make "variants" whiout break from other scene reference.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

I think the example above explain it.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and / or diagrams

I don't know how to make, but i know this will help most of designers.

If this enhancement will not be used often, can it be worked around with a few lines of script?

I do not think so. I know that some designs will love use this feature often.

Is there a reason why this should be core and not an add-on in the asset library?

I do not think so.

[sttifer]

Sorry, i didn't saw that Godot have this feature ("New Inherited Scene"):