I think #2 and 3 are like tryng to shove toothpaste back into the tube.
#1 is possible but doesn’t take human nature into account. Take the subject of marriage away for a second. Call it pet licenses. Say that everyone needs to license their cat or dog. Then suddenly a bunch of people come up wanting to license their frogs and weasels. So a new law is passed to allow anyone to license any animal. Some cat and dog owners don’t enjoy it. But the majority of people don’t really care. The cat and dog owners want to get rid of pet licenses altogether, just have people owning animals without needing a license. Yes, it would work. But there just isn’t enough pressure for a fight.
Disagree, since a pet license isn’t really comparable to the sacred institution of marriage (for most religious people including Christians, and even for a sizable minority of secular individuals).
This IS a fight that isn’t going away, and it would be considerably easier to attack all the ways that government has control over “marriage”.
The hardest for conservatives to fight would obviously be the issue of ‘Who gets to raise’ children.