I think we should also default to no license selected instead of MIT (and make a valid license selection mandatory to validate an edit).
Currently too many users use MIT just because it's the default choice, and usually don't reflect that info in their git repository. We could link to http://choosealicense.com/ and mention that users should add a LICENSE file in their repo matching the license they pick on the assetlib.
Quoting @akien-mga from https://github.com/godotengine/godot-asset-library/issues/133#issuecomment-374503302: