People have talked about guild houses, in game books, and even guild libraries. I also know that there are people who have started their own servers and who have made their own maps.
So I'm thinking, what if someone made a game which was just a single zone, and maybe that zone was just the interior of a building? That is, it's as if you entered that building and are now trapped in it. That building could be a library complete with books written by players. If you wanted a guild library for instance, each guild could have their own version of this game personalized with their own texts. Basically, you would download the game, and when you play it you become your character exploring the library of your guild.
The game would not need to be multiplayer, but a multiplayer version could exist for those lucky enough to have a dedicated server of their own. The books could be stored as text files in a data directory with names such as book1.txt, book2.txt, etcetera. To add books, you would simply edit a placeholder text file.
I think that people would have fun with it. The next question is whether or not there's someone with enough skill and interest to experiment with it?