Just as some case:
A map editor;
A tool to make mod base on game engine

The main idea is, start the mod can be seen as start an individual "game", the game may without world, without character, without items, or just with nothing waiting user to build itself.

This could be enter from a button on start menu. And for the cases, start a game obj may be useless and make things more complex.

The original idea is to make a tool do translation easier with GUI support, with some input textfields, shown as a table like:

translation.id | english base | example sentence generated from game | translated ones | translated preview

and some func like reload mod, export file, compare with old version to make updates.

(This logic is not too complex to do and I have implemented some with python scripts, but generate example sentence can not done without internal mod supported, and as a tool, GUI integrate with base game should be cool)