Developers should be able to easily create a new GUI. This should include an easy and straight forward way to make TileEntities for containers.
Add slots, text, buttons, and other features (furnace) to GUIs, and containers
Justification and Use Case:
The ability to create new GUIs easily would allow for new types of blocks with GUIs; this helps because in a lot of mods, the current systems of turning items into other ones might not fit with the mod. Instead, new ways of item conversion could be made that fit with mods.