> To be clear, I would love a simple Japan-style federal zoning code.
Japan doesn't really have a "federal zoning code", because Japan isn't a federation, it is a unitary state. Japan's prefectures aren't states. In a federal system, such as the Australia, Brazil, Canada, India, Germany, Mexico, Switzerland or the US, the constitution grants certain powers to the federal government and the states generally retain the rest. By contrast, in a unitary system, the national government retains all power, but may choose to delegate certain powers to subnational divisions, such as Japan's prefectures. Japan's prefectures are delegated responsibility for certain functions. They don't have general powers of legislation, only the power to make subsidiary laws on certain specific topics where national law grants them that authority. Japan's prefectures are actually just the first tier of Japan's two tiers of local government. There is a proposal to convert Japan into a proper federation (Dōshūsei, 道州制), by creating states/provinces as a new level of government in between the prefectures and national government (except for the prefecture of Hokkaido, which would become a state/province). However, although there is somewhat of a consensus in Japanese politics in support of this idea in principle, in practice not much progress has been made–I believe in part due to disagreements over exactly how many states/provinces to create, what should be their boundaries, and exactly what powers they should have.
The distribution of powers between the state and federal levels is different in every federation. For example, in Canada, Germany and India, enacting criminal law is a federal responsibility, and states lack the power to make their own criminal law, but they still play a major role in its enforcement; by contrast, in Australia and the US, every state has its own criminal law, with state and federal criminal law working in parallel. So there is no reason why, even in a federal system, you couldn't give the federal government powers over zoning. In practice, however, I'm not aware of any country in which that has happened. In most federal systems, zoning law is a state or local responsibility, and a constitutional amendment could be required to transfer that power to the federal level.
In Australia, there is a process called referral by which states can voluntarily transfer certain powers to the federal level, without requiring a constitutional amendment. In principle, Australia could adopt a federal zoning law, without changing the constitution, if every state passed a law referring that authority to the federal level. A state can unilaterally take back the power at any time by repealing its referral law. Never been used for zoning, and I doubt it ever would be, but it has been used in some areas of law – for example, it was used to establish Australia's uniform national corporations law. However, I don't know if that would work in the US, since while Australia's constitution explicitly says you can do this, the US constitution doesn't. Even were the Supreme Court to rule that "states can voluntarily delegate powers to Congress even without an explicit constitutional provision to authorise it", it is a lot easier to get every state to agree on something when you only have 6 as opposed to 50.
Another option would be a uniform law, instead of a federal law – in which every state voluntarily chooses to enact the same law. A famous example in the US is the Uniform Commercial Code. No reason in theory why you couldn't have a Uniform Zoning Code to go with it, but I doubt you'd ever get all 50 states to agree on its contents. Consensus is much easier in commercial law because it is the kind of dry legal area in which few people really care about the details, and few people would be impacted by different options as to what those details are
Japan doesn't really have a "federal zoning code", because Japan isn't a federation, it is a unitary state. Japan's prefectures aren't states. In a federal system, such as the Australia, Brazil, Canada, India, Germany, Mexico, Switzerland or the US, the constitution grants certain powers to the federal government and the states generally retain the rest. By contrast, in a unitary system, the national government retains all power, but may choose to delegate certain powers to subnational divisions, such as Japan's prefectures. Japan's prefectures are delegated responsibility for certain functions. They don't have general powers of legislation, only the power to make subsidiary laws on certain specific topics where national law grants them that authority. Japan's prefectures are actually just the first tier of Japan's two tiers of local government. There is a proposal to convert Japan into a proper federation (Dōshūsei, 道州制), by creating states/provinces as a new level of government in between the prefectures and national government (except for the prefecture of Hokkaido, which would become a state/province). However, although there is somewhat of a consensus in Japanese politics in support of this idea in principle, in practice not much progress has been made–I believe in part due to disagreements over exactly how many states/provinces to create, what should be their boundaries, and exactly what powers they should have.
The distribution of powers between the state and federal levels is different in every federation. For example, in Canada, Germany and India, enacting criminal law is a federal responsibility, and states lack the power to make their own criminal law, but they still play a major role in its enforcement; by contrast, in Australia and the US, every state has its own criminal law, with state and federal criminal law working in parallel. So there is no reason why, even in a federal system, you couldn't give the federal government powers over zoning. In practice, however, I'm not aware of any country in which that has happened. In most federal systems, zoning law is a state or local responsibility, and a constitutional amendment could be required to transfer that power to the federal level.
In Australia, there is a process called referral by which states can voluntarily transfer certain powers to the federal level, without requiring a constitutional amendment. In principle, Australia could adopt a federal zoning law, without changing the constitution, if every state passed a law referring that authority to the federal level. A state can unilaterally take back the power at any time by repealing its referral law. Never been used for zoning, and I doubt it ever would be, but it has been used in some areas of law – for example, it was used to establish Australia's uniform national corporations law. However, I don't know if that would work in the US, since while Australia's constitution explicitly says you can do this, the US constitution doesn't. Even were the Supreme Court to rule that "states can voluntarily delegate powers to Congress even without an explicit constitutional provision to authorise it", it is a lot easier to get every state to agree on something when you only have 6 as opposed to 50.
Another option would be a uniform law, instead of a federal law – in which every state voluntarily chooses to enact the same law. A famous example in the US is the Uniform Commercial Code. No reason in theory why you couldn't have a Uniform Zoning Code to go with it, but I doubt you'd ever get all 50 states to agree on its contents. Consensus is much easier in commercial law because it is the kind of dry legal area in which few people really care about the details, and few people would be impacted by different options as to what those details are