Minnesota has done the right thing. Seeing the overwhelming voter turnout for the 2016 Presidential caucus races, Minnesota will switch to a Presidential primary system for the 2020 Presidential race.
One assumes that both the Minnesota Republican Presidential Race and the Minnesota Democrat Presidential Race will be primaries. And, those voting in 2020 will have to declare as either supporting a republican or democrat party credo. That may drive Sanders supporters nuts.
Eventually I can can envision the Republican and Democrat parties splitting into two additional categories, Independent Democrat, Independent Republican. Presidential Candidates can register in one of the four categories and then the top Republican and top Democrat category vie for the presidency in November.
If this scenario had been in play this year, Trump would have been the Independent Republican candidate, Sanders the Independent Democrat Candidate. Based on vote totals, the fall presidential election would pit Independent Republican Donald Trump against Democrat Candidate Hillary Clinton.