A gay marriage nationalization decision, as unpopular as it would poll when handed down, wouldn’t be likely to be overturned by amendment. It would take at least four years of single-issue-voter elections to get the votes in the Senate for the amendment (67 needed, no more than 45 now in hand), and approval by the states is simply not going to happen. Only 13 have to reject to defeat it, and it will in at least 8 or 9 eastern seaboard states, and in at least 5 or 6 western states (liberal and/or libertarian alike).
It probably won’t even be seriously pushed. Every winning coalition in politics is an alliance of elite and popular interests. No elites can be in common cause with anti-gay-marriage dead-enders after opposition to gay marriage becomes regarded as unacceptable bigotry where the elite live and work, something that will take place almost immediately after the decision is handed down.
However, if any marriage amendment passes muster, it won't be one that's convoluted. It will be one that simply defines marriage once and for all.