There are too many factors involved in this to make any reasonable prediction. Demographic changes have undeniably rattled the GOP; that's the real motivation behind their unsubstantiated accusations of massive voter fraud, which they're using to justify disenfranchisement of the disadvantaged (which skews low-income, i.e. predominantly minority and young). White Americans have shown disproportionate electoral power - particularly those who're upper income and older, which are the GOP's base. Democrats underperform in elections when voter turnout is low; thus, to extend their electoral chances, the GOP has engaged in gerrymandering, implemented voter ID laws, and attempted to stifle early voting and same-day registration.
However, we cannot only fault Republicans for this, nor will these tactics save them in the long-term. Democrats are at least equally responsible for the lack of voter enthusiasm due to uninspiring policies (despite Clinton's emphasis on social justice issues, she won fewer African American and Hispanic votes than Obama, and turnout was lower) and the party's disconnect from working class voters of all races. Minorities are disproportionately lower and working class, as are Millennials; the party must focus on issues that resonate with their lived experiences and daily struggles. There is also the absurd notion adopted by many on the left today that somehow a college degree translates into class; there is a growing number of working class persons with college degrees, just as there are tens of millions of upper-class Americans without a degree. Equally important as class is the issues of financial and employment insecurity, chronic low wages, difficulty entering the job market, and the high cost of living (particularly in the locations where the most jobs are located).
Unless Democrats can both reverse the disenfranchisement motivated gerrymandering and voter suppression policies of the GOP, and reconnect with the working class of all races, the Republicans will continue to wield increasingly disproportionate control over local, state, and national government. So, even with significant demographic changes, they can reduce the impacts of those changes and buy themselves more time. Of course, that will be nothing more than an interim period before the Republicans are forced to shift towards incorporating affluent and assimilated members of minority groups into their coalition. In the meantime, Democrats will need to focus on turning out working class, Millennial, minority, and urban voters.
Democrats did gerrymander in the 1970's and 1980's too. I am for redistricting reform but neither party will do it.
