With legalisation of same sex marriage in Australia in the news again, it's interesting to see NPR reports on a new Pew survey result showing that, in the US, public approval of legalising it is still on the rise:
And even Republicans have weakened in opposition:
I guess it's a factor of former opponents not seeing the world change much around them after it's legalised. There's no reason to believe it wouldn't happen similarly in Australia.
That said, a defensible conservative position remains to have civil unions for those who want the equivalent rights as heterosexual marriage, but which leave millennial long understandings of the meaning of "marriage" alone.