Eventually, the weird alliance between rich urban Whites and racial minorities that is the Democratic Party will break under its own weight, and the GOP will gain substantially with rural minorities (Blacks in the South) and working-class Latinos. The GOP can achieve this by becoming even "Trumpier" in the extent that it continues to make bogeymen out of neoliberal types.
In the long term, the current political alignment will reach its apogee when White voters in the Midwest are just as partisan as Whites in the South.
How on Earth do the Dems win control of the federal government or even the presidency in that environment?
The exodus of minorities from the Dems is probably what will signify the end of the current alignment and the beginning of the next one. In the meantime, Democrats can expect to continue to improve with college educated Whites. Non-college educated Whites will continue to constitute less and less of the electorate. Thechrrent alignment is favorable to Democrats (at least in the popular vote), the next one should favor the GOP.