Idea: Allow a world exclusively for experimenting with few restrictions and adapted for a different type of gameplay.
Details: The Sandbox world would allow users to place any buildings, and any GB without requiring goods. Diamonds would be unavailable from quests, but would still be available to buy for premium buildings. Forge Points would cost only 10 coins each, and all expansions would be available for 1000 coins each. Houses would continue to operate as usual, as would goods and supply buildings. (These are just suggestions, please don't downrate the whole idea based on one of these.)
Abuse: No abuse. Diamonds would cost the same, and would be unavailable on quests, meaning that there would be no effect on other worlds. There would need to be some change to the ranking system, perhaps abolishing it completely.