@Alon @kentwillard Re the paper, diachronic is too nonspecific for me to really understand or comment about.

Re the spatial correlation, yes. But then progressive just become a geographically segregated faction in a zero-sum game to have its interests looked after. That's what we want to avoid. Rewarding migration without accommodating and somehow coopting into a forward-looking politics those who remain exacerbates zero-sum factionalism, rather than coparticipation in a shared, joint project.