I have limited experience scripting Blender, but there is a BPY API to add custom panels, so adding metadata to “entities” and simplifying the export workflow is probably feasible to the point it will be very close to an editor.
And of course since Blender is used for movies, it does scenes well already.
Really depends on the team size, composition, and game. If you have designers on the team who aren't dedicated programmers, I don't think blender will cut it for them.
The demands of a movie differ from a game which is why I'm a bit doubtful. But nothing is impossible to achieve with peope planning, so I'm not dismissing it.
At least when I last tried Blender the UI was a lot harder to use than something like Unreal or Unity editor.
I'd probably look at the Godot editor first.
But I do like the idea of trying to find an existing editor in the same domain and modifying that rather than building from scratch.
The key to making no engine work is to make only what you actually need.