I had plans for making a scripting system for Net Mission after I finished the racing game... But then it hit me that it would be extremely awesome to make it now.
If you're unfamiliar with what a scripting system is, it's basically a system that reads and executes a series of instructions. It's slower than just compiling the instructions as code, but I'm trying my best to get it as fast as possible.
So I've thought up ways to make all of the game content stored as scripts, and that's what I'm working on next. What's cool about this approach is that I can make tons of useful engine features in C++ and then use them in an editor for the game.
This would help immensely to quickly expand the game's possibilities if I can get it done. For example, in collision response, an object's response to a collision can just be a script. So each object could have different reactions to collisions with different things.
If you need an analogy... I'm basically making Game/RPG Maker for action-based sidescrollers. But not only can I open up Sidescroller Maker and work on my game in it, but I also have control over Sidescroller Maker itself. "Oh hum, I want a function to spawn my creature over here." *makes the function*
I already have a decent start on it. The biggest obstacles are reorganizing my engine a little and making the editor. The scripting itself is working.