One thing that really needs to be addressed is how to retrofit the glut of car-centric developments designed in the late 20th century, to better conform with the growing sense of value we have in walkable communities today. Navigating the minefield of local zoning politics to try and convert car-centric stripmall mcmansion suburbs into tighter village-like communities will be an enduring puzzle in America at least.

There's also an interesting question in what happens when we cluster too many people into one city based around talent markets for knowledge work.

The Brexit vote in England may well be partially the result of the fact that the younger workforce in the UK was all stuffed into London due to the high concentration of knowledge work employers there, preventing newer ideas and values from being evenly applied across more of the country. You see the same thing happening in the USA, with near total dominance of one political ideology in the larger coastal cities and dominance of the other in places further afield. We're seeing a reversion to city-states in this regard, and with the distributed nature of knowledge work, you'd expect to see the opposite happening...