The Millennials and Gen Z are the least civically-involved generations in the history of the republic. Upon what basis he and others think this is going to reverse is something they need to explain.
The second faulty premise in his fantasy world is that brown people will vote almost entirely Democratic. As we saw in the presidential election, "Hispanic" voters are not so predictable and many of them have great qualms with the left agenda. Not to mention that this coalition of the oppressed is hardly a harmonious amalgam.