The only one of those megaregions that's really a tenable megaregion is the Northeast Corridor, which is (unsurprisingly) the genesis of the term in the first p

The only one of those megaregions that's really a tenable megaregion is the Northeast Corridor, which is (unsurprisingly) the genesis of the term in the first place. Traveling from DC to Boston, there's not really any point where you escape to rural areas, and several metropolitan areas blend to the point where drawing lines between them doesn't make sense (Baltimore-Washington in particular). Outside of the Northeast, the megaregions don't really play out. Chicago, Los Angeles, and the Bay Area are all cases where you have a dominant MSA with surrounding MSAs that are essentially dependent on the core MSA, with continuous sprawl between them. But it's not entirely the same dynamic as the Northeast region, although in terms of having a headquarters that people can occasionally visit in person, it works. The Gulf Coast, Cascadia, and Front Range megaregions that are identified are, quite frankly, fantasy that feels like an attempt to stuff as many people into megaregions as possible.