The reason that Gay marriage has gotten so much traction is that traditional marriage has become de-linked from child-rearing already. IOW’s society no longer accepts the basic assumption of the family unit based on a married couple. So why not Gay marriage? (or any other alternate interpretations of the institution?)
I think the hip-gay on the hit TV sitcom is more a symptom of family decline than an underlying cause. But going forward you might be more right. Everything is a feed-back loop.
“...why not gay marriage..”
We are done. Christianity attempted to raise women to equal status. Even if a person is not Christian, that capital rode for many centuries for the benefit of many, even if they had not clue as to why.