Just following up on what the U.S. Constitution has to say about my idea of a metro area seeking to become a state:

New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.

Hmm, so if the Philadelphia metro area (which includes parts of Pennsylvania, New Jersey, and Delaware) wanted to become its own State, it would need to sell all three existing states and the U.S. Congress on the idea. It sounds far-fetched. Then again, rural voters are often under the mistaken impression that they are subsidizing urban areas, even though the evidence proves that the exact opposite is the case. So if Philadelphia wanted to leave Pennsylvania for New Jersey, and it were put to a referendum, people might go for it. Electoral votes would be a potential sticking point, so getting rid of the Electoral College could help make something like this slightly more plausible. It still sounds implausible under our current (241 years and counting) Constitution. Still, there could be enormous advantages to a metro area controlling its own tax policy, housing policy, infrastructure policy, environmental policy, etc.