exclusivity isn't unenlightened (etc.)

I agree that society has made progress in no longer attaching such a heavy weight to female virginity, for instance. I am fine with women choosing sexual behaviors that work for them.

It is still a widespread expectation that adult relationships are exclusive at a given time. I think that is a reasonable expectation and not just insufficient enlightenment, though I have no problem with those who choose open relationships.

The changed society I was imagining was one where your small girl engaged in oral sex when asked because it was expected of her, not because she inherently wanted it. And there was doing it in public. For me, those are disturbing hypothetical developments and not just more hurdles to be overcoming in the struggle against sexism or prudishness.

As for the bottom dropping out of prostitution

Wikipedia as of today doesn't treat this as a fact (https://en.wikipedia.org/wiki/Prostitution#Prevalence):

"Reports disagree on whether prostitution levels are growing or declining in developed countries."