Just an idea that you're probably not ready for, but it might be worth considering some kind of plugin architecture, either for items, the map, and/or the player.
The benefit being that the code can become more modular, allowing you and others who wish to contribute to do so without kludging up the 'engine'.
The main Issue in Minecraft is the API system build around those various system (Forge etc...) I think that this project can grow with a better Plugin system as @moonsspoon suggested.
Just an idea that you're probably not ready for, but it might be worth considering some kind of plugin architecture, either for items, the map, and/or the player.
The benefit being that the code can become more modular, allowing you and others who wish to contribute to do so without kludging up the 'engine'.