These type of "demographic destiny" predictions frequently get proven wrong. Although you can understand the desperation on the side of Team Blue to actually win something...Part of the problem for Democrats is that they have been reduced to coastal and metropolitan enclaves where their identity politics play well within the cultural and media echo chambers that dominate. Their leadership are old and the party has almost no new ideas outside Bernie Sanders.  They need to find a message that resonates with the rest of the country - this is far more significant. 

With the rates of inter-marriage increasing every year and economic mobility improving (mostly in Red states where a great internal migration is taking place) terms like "white" and "middle class" votes becomes increasingly blurred. Trump and the GOP won because they could appeal to the working class and "rest of America"; not because of redistricting - even the Blue Wall could not stop this reality.