At this stage, could the GOP nominate an openly gay candidate as President?

[MarkD]

The fact that a candidate IS gay is not what would be most important to the rank-and-file voters of the Republican party, but whether the gay candidate would support and help advance the cause of gay equality. Sometimes an openly gay person does not make any issue out of their desire for equal rights, and is accused by gay left-wingers of being a "lavender Uncle Tom" or even being like a Jew who helps Nazis. An openly gay candidate like that could be quite acceptable to Republican voters.
Also, what kind of people would the gay candidate intend to appoint to the Supreme Court? Advocates for original intent? That would be another reason for Republican voters to support such a candidate, and for gay lefties to loathe the candidate.