importlib/_bootstrap.py is importlib, period, so there is no separation of what is used to start Python and what is used after interpreter startup is completed.

As for adding a 'stat' argument to the loaders, it's possible but as always it comes down to whether it will break someone or not. Since loaders do not necessarily execute immediately you are running the risk of a very stale cached stat object. Plus Eric Snow has his PEP where the API in terms of loader __init__ signature so you would want to look into that.