I think this isn’t what most people assume. Currently, the 360 requires the disc to authenticate even if you’ve installed the game to the HDD.

Assuming the disc ID is stored along with the installed copy, what if the One had different modes of operation:

1. If the disc is detected and stays in the drive, no authentication is required.
2. If the disc is not detected, but the game has been installed: If you have activated the disc on your account, you can play.
3. If the disc is not detected, but the game has been installed: If you have not activated the disc on your account, you can pay to activate, and a new disc ID is associated with your installed copy.

This way, used physical games are still feasible.

But no games can be played from the disc; all games require an install.

Maybe you don’t need to authenticate if you’ve got the disc? Then it makes sense, because if you don’t have the disc, you’ve likely sold your game.

Proves that things can always get worse.

The post-completion gameplay in AC3 featured a different “vessel” character for the Animus.
The voice actor for the character and the operator were totally new.