> It wouldn't take much. Just having the assets loaded at runtime instead of being hardcoded should be enough to get some people started.

I'm not familiar with Jeff's code, but I do work in game development, and something like this would likely be a huge undertaking, and would affect pretty much every aspect of the game.

Optimisation #0 for loading times is compress a gigantic pile of stuff into a giant binary blob, and index it at runtime. Undoing that to support custom content would be a huge time investment on any of the games I've worked on.