If/when depolarization happens, what will it look like?

[Alcibiades]

I disagree. The U.S. has almost always exhibited some degree of political polarization, but our current era of such is largely related to economic pressures resulting from income inequality, which drives citizens to choose more ideologically-extreme options. This chart shows the share of pre-tax household income received by the top 1%, top 0.1%, & top 0.01% in the U.S.:



As we can see, the level of income inequality mirrors the level of political polarization: if you look at the beginning of the charts (so, the late-1800s & early-1900s), levels of political polarization & income inequality were high. This obviously coincides with the Gilded Age, an era known for its lack of substantive business-structure regulation & labor laws in spite of there being massive industrial growth. This subjected much of the working-poor to harsh-working conditions & allowed the elite to gain untold riches. This - along with an often jingoistic & dis-informative press - radicalized the 2 flanks of the population until progressive reforms were enacted under Teddy Roosevelt. Polarization later rose slightly during WWI & the year after due to the 1st Red Scare, but decreased during the Roaring Twenties & continued to do so even further when FDR enacted the New Deal in response to the Depression, which further reduced income inequality.

Any of this sound familiar? Well, we're obviously currently in a 2nd Gilded Age, triggered by the ideology of seemingly-perpetual deregulatory reforms that were initiated in the 1970s & cuts to social-spending (outside of health-care) that culminated in Clinton's passage of "the end of welfare as we know it." In the social-issue realm, one of these deregulatory reforms was the 1987 abolition of the FCC's Fairness Doctrine, which required all news broadcasters to report only the facts with as little bias as possible. This led to the rise of conservative talk-radio & the subsequent moral panics of the late '80s & early '90s. At that point in the first chart, we can see polarization begin its climb to its current levels today. This was made even worse by the infamous Citizens United case, which allowed unlimited amounts of corporate PAC money to pour into our elections. This - combined with the fact that the average American family never really recovered from the Great Recession - has created an immense amount of pressure &, in turn, radicalization.

I find this somewhat funny because the only other person who I have heard basically calling this era a 2nd Gilded Age is Tucker Carlson. And I imagine that in all likelihood you loathe Carlson.
In any case, it's a theory to which I probably subscribe.

Thomas Piketty and Paul Krugman have also described it as such. The latter said, “The middle class America of my youth is best not thought of as the normal state of our society, but as an interregnum between Gilded Ages.” In this way, the New Deal order with its profound economic, social and political effects, reducing both economic equality and political polarisation, was arguably an aberration within American history.

[Alcibiades]

I don't think you'll get a "socially liberal" Republican; you will get a socially tolerant Republican.  John Kasich is a social conservative through and through ... yet he has tons of issues with Trump's rhetoric (on the record, anyway).  Any "GOP Clinton" will likely be a reaction to Democratic control for an extended period of time, as the Democratic Party exerts its power to enact progressive legislation.  Such a GOP nominee would hold together culturally and socially conservative voters, economic conservatives and regain several moderate areas, most likely in the suburbs.

Everyone stereotypes middle- and upper-middle class voters who have fled the GOP as "socially liberal," but they're not from my experience.  They like stability.  In the right climate, that is as socially conservative as it is socially liberal ... Trump is just giving "social conservatism" a very demagogic and unsavory face, bordering on reactionary appeal.

It's been four years and Atlas still doesn't get that fiscon-soclib barely exists outside the internet.

There is a misconeption that wealthy suburbs have shifted to the Democrats as more fiscon/soclibs enter the party. Rather, the main reason is that the suburbs have become more liberal on both social and economic issues.