It sounds like these aren't people fleeing the blue states who end up voting for Democrats. Rather they're young people moving where the jobs are and bringing their political views with them. I suspect they don't have serious ideological grievances with the places they came from. People who really don't like the blue states and move to red states may get scapegoated for the failure of Republicans in those states to adapt their ways to changing demographics.
But according to the Stanford political scientist Jonathan Rodden’s new book, Why Cities Lose, the problem isn’t just the districting. It’s the density. All over the world, liberal, college-educated voters pack into cities, where they dilute their own voting power through excessive concentration. “Underrepresentation of the urban left in national legislatures and governments has been a basic feature of all industrialized countries that use winner-take-all elections,” he writes.
Far be it from me to argue with a Stanford political scientist, but no. The people he's talking about are something like 10% of the population, maybe a little more. If they win anything at all it's because they are concentrated. Spread them out equally across the country and their votes wouldn't count for much.
The mistake is that one assumes that voting patterns among millenials will always remain static. At some time they will grow up and possibly think and vote differently especially if they have kids.