DOMA actively breaks the commerce clause. If this is finally overturned, all states will de facto permit gay marriage, since a contract signed in one state is valid in all states. And in fact we already have a domestic partnership license - your suggestion that we create a separate but equal license for SSM has been tried for 2 decades with violent opposition from teh american taliban. The simplest and most economical solution is to simply allow gay marriage, since it in no way effects you.
Or is this really about something else for you?