Will the world ever be ready for a gay president?
No, not in the next few decades. And you need to distinguish "world" from the US.
The world hailed the first Black US President. Whereas our own US Republicans hate a N***er being in their "White" House. They're doing everything they can to sabotage his Presidency, regardless of the cost to the nation. Just so long as a White Republican replaces him, backed by a White Republican Congress and a White Federal Court system.
Should a gay be elected to be President, you can expect the same Republican sabotage. All in the name of Jesus and family values.
Nor could much of the world welcome a gay US President. Muslims could not, and they're like a quarter of the population. Roman Catholics could not, and they're another billion-plus. Not sure about China, well over a billion there. Traditionally anti-gay, they may be realizing that accepting LGBT may help their overpopulation problem, as effectively as their failed 1-child policy.
Of course this would give US homophobes more ammunition, that we shouldn't copy the godless "Commies". Problem for them is Putin's homophobic Commie Russia, and the Africa of their own making. Be interesting to see how this develops.
But in any case, Right Wingers would try to sabotage a gay US President, just like they have a Black President. Be a straight White Protestant male or fail.