I had this idea to implement achievements that could be unique to each player.
The primary reason I thought of this was to help facilitate the control and distribution of DLC, but I’m sure this can be used in other ways as well.
Let’s say you have a hidden achievement called Expansion Pack, and the game was coded to the effect of… if we have this achievement, then do stuff. In fact, there could be an internal check for “unique achievements” so that game designers wouldn’t have to worry about coding this in. All they’d have to do is something like
*unique_achievement instead of
Back on the game, there could be an Purchase/Activate DLC button that communicates with a server and lets you type in your purchase receipt number (this process can be automated as well, I believe).
That purchase receipt number could then become a part of the name of your achievement, something like… Expansion Pack 1: (receipt number here).