How about a dual authentication approach which gives an option of:
-either registering your game with PSN which enables disc free play
-or not registering the game and instead require the game disc in the drive for authentication.
If you registered and then lent your game to a friend you wouldn't need to deactivate the game on the PSN, your friend would be able to play simply by having the disc in the drive.
Though a slight problem with above would be the inevitable abuse on the 2nd hand market where some SOB would sell a game without deactivating his copy, denying disc free play to the second owner.
-either registering your game with PSN which enables disc free play
-or not registering the game and instead require the game disc in the drive for authentication.
If you registered and then lent your game to a friend you wouldn't need to deactivate the game on the PSN, your friend would be able to play simply by having the disc in the drive.
Though a slight problem with above would be the inevitable abuse on the 2nd hand market where some SOB would sell a game without deactivating his copy, denying disc free play to the second owner.