Interesting points, but methinks you have made it to complicated. Unless government intervenes, marriage remains one man and one woman.
Thanks
A while ago the government decided that home ownership was a good thing. So they decided to give all sorts of benefits to homeowners such as tax deductions on interest, no capital gains tax when a house is sold, creation of Fannie Mae and Freddie Mac to give banks more reason to make more home loans than they otherwise would, etc.
The end result was the housing bubble and crash of 2006.
A while ago the government decided that marriage between a man and a woman was a good thing. So they decided to give all sorts of benefits to married couples such as special visitation rights, implied powers of attorneys, special rights and responsibilities with regard to their children, special treatment when one of the spouses dies, etc. This could all have been handled by contract law. The couples could have been required to spend money on lawyers to acquire all of the rights and responsibilities that the government gave them for free by law. But the married couples wanted the freebies. So along come the gays who want the same freebies and the whole house of cards collapses. Either you have to get the government completely out and require heterosexual married couples to spend hundreds or thousands of dollars in lawyers fees to grant themselves the rights they now have by law for free, or you have to give all the same goodies to gay couples.
It would be really nice if life was as simple as you hoped it would be, but that train left the station almost a hundred years ago ... or more.