I propose someone creates an in game program editor, similar to Expression 2 for anyone that plays Garry's Mod. This would allow people to create almost anything imaginable, using no redstone. You could create models from within the editor, and program an AI for them, so basically you could create your own mobs. Or, you could create items, with special properties. This would be a rather large mod, but I think it would make the game much more fun, and would expand the modding community.
You couldn't do a LOT with it, but I suppose you could create some sort of item creator. It would have limited choices, as each choice you have adds a whole new combination of items that you have to pre-create.
Well, if you coded the item from scratch, you could also set the icon for the item as binary data. You could also create little minigames and stuff with it.
Minecraft In Game Programming