In my other comment responding to this parent comment, I linked to an article where Five Thirty Eight was doing statistical analysis on Harris’s potential performance: and they said that both Harris and Biden were hurt by being insufficiently moderate and doing poorly with moderates. But even aside from that, my expectation is that if the Democratic Party picks a candidate with the explicit goal of winning the general election, it’s most-likely going to be, if anything and given the freedom to do so, shifting more-centrist from where things are today, not further to the left. The primary system will tend to pick candidates that are further from the center than would be an optimal choice from a strategic voting standpoint, since you want a candidate that will win (which includes appealing to swing voters), not the most-favored candidate by voters who vote in the party primary.

I would assume that the party would further optimize to win in the Electoral College, so from a party-chosen candidate, I’d expect to see someone that would disproportionately look like a swing voter in a swing state would want. You’d want someone that would look good to someone who is undecided between the Republican and Democratic ticket in Michigan or Wisconsin, say. A purple voter in a purple state.