Square Enix: Yes, you will need to have registered the Expansion to access the characters or any other thing that is related to the Endwalker Expansion.
Me: Okay so until my escalated ticket is resolved, I can't access the game after today?
Square Enix: You should be able to access the game, but not the Endwalker Expansion related Items, Characters, etc.
Looks like its just limited to Endwalker.