Thought this Slate article on the UAE was worth Federalists pondering. Particularly:
"It's a federation of seven somewhat autonomous sheikdoms—Abu Dhabi, Dubai, Sharjah, Ajman, Umm al-Qaiwain, Ras al-Khaimah, and Fujairah. Under the country's constitution, each emirate maintains principal control of its own oil revenues and other natural resources. They turn over a set percentage of their revenues to the federal government, which takes care of defense, diplomacy, education, public health, banking, and several other concerns for everyone. But that's the extent of it: The constitution gives each emirate explicit and exclusive control over any matter not specifically assigned to the federation. For example, a conservative emirate like Sharjah has the right to institute its especially strict code of decency, which prohibits bathing suits, midriffs, and skirts above the knee."
Unlike some federal systems (eg Russia), this one has real teeth: the component parts have bargaining power with the federal government. Japan is a unitary state, so by contrast there is little possibility of experimentation regionally; the Japanese generally must get fresh policy ideas from abroad.