Player-driven-development
I've recently got back into hacking on Endarchy, mostly focusing on infrastructural level stuff since I don't have a place to run it at the moment.
An aspect I'd like to explore is player-driven extensibility. UrbanDead fans have contributed a lot of extensions and ideas for improvements; I'd love to see an UrbanDead-like game where the players can do more of this sort of stuff from inside the game.
So far I've added some crude "terraforming" functionality for editing the game map in-game. But currently I'm working on a "blueprint" system to allow players to define new objects and effects they generate (allowing putting fuel in generators, that sort of stuff). I think I may be able to implement most of the game rules using blueprints. Making the game logic data-driven would be handy since game changes wouldn't always require code roll outs or database sql changes.