I can't see this happening. The Democrats would be a party that is economically neoliberal, socially SJW, and foreign policy neoconservative--it's like a mashup of all the least popular political views.
Except that really is the direction of the Democratic Party and the 1%. Places like Goldman Sachs and JP Morgan are crawling with SJWs and SJWism.
Being the party of Goldman Sachs is viable. After all, Hillary's doing it right now and she'll win the nomination. It's the socioeconomic agenda of white elites, supported by a large mass of minorities that you keep in the party through racial issues like BLM.
I think this will depend on whether or not the economy can improve and the educated but underemployed millennials of today can eventually find well-paying jobs, buy homes and start families like the baby boomers were able to.
There is pretty much no way that will ever happen. Recessions permanently damage the incomes, physical health, mental health, social health of generations that grow up under them. The current generation of millennials will never have any of those things; even if the economy manages to recover (which it probably won't), the beneficiaries will almost entirely be the (smaller) generation AFTER the millennials.
The millennial generation is basically permanently socially destroyed, somewhat reminiscent of the Lost Generation after World War I. The 90% of millennials who voted for Bernie are still going to be socialists in 30 years - if anything, they will probably radicalize as things do not improve for them (since most millennials are delusionally optimistic about their futures.)
Just the sheer demographic weight of this generation means that the real political question is what kind of socialism triumphs in America. Left-socialism or Trumpism.
