It's interesting that 20 years later—despite modern games all essentially have a "shared" save data space—the only games I can actually recall taking advantage of that are the BK/BT rereleases on Xbox.* If a game were to do this today, I would probably still think it's extremely cool. But why do that when they could sell you the unlockable instead.
[COLOR="Gray"]*I'm sure consoles have software restrictions in place to prevent one game from wrecking havoc with another game's data. If they're anything like iOS, though, software from a developer could read and write data of another piece of software by the same developer.