I think Democrats won't move to the left economically, they're destined to become a Fairfax County-type party IMO. Not sure about the GOP, populism or Trumpism (and let's not forget that Trump has basically been governing like a generic R so far, with one or two exceptions like that stupid executive order) alone won't be a winning strategy in the long term. They'll have to combine it with something else. The party will probably be pretty fractured, not that that's necessarily a bad thing.
I'm oh-so skeptical of this. They're far from that type of party now, and I think they're smart enough to know they'd win about 30% of the vote being such a party.
Last time I checked Hillary Clinton won the PV with 48% of the vote, not 30%. Democrats will always have a floor of 46%/47% or so because of White liberals and minority voters.