So what is going to happen?
I suspect that a couple married in a same-sex friendly state will move to a same-sex unfriendly state and begin to say, for legal purposes, that they are married.
The new state will tell them no they aren't, based on their own law and policy as protected under the DoMA.
The married couple will sue. This will all be shopped around to a state with a receptive court system and federal circuit. It will go all the way to the USSC who will decide, probnably in a close decision, that the DoMA is unconstitutional in that it serves no important state purpose to deny the recognition to a married couple based on their same-sex status, primarily out of a combination of equal protection grounds and full faith and credit issues.
Unless a constitutional amendment takes the issue away.
In the case of a gun permits across jurisdictions, there wouldn't be the same (or even a similar) equal protection and full faith & credit issue. There would be a 1st amendment issue I suppose but that has all been settled from tradition & custom over the decades.
As far as tradition and custom goes, some might suggest that there is no tradition or custom for same sex marriage. That's true, but there is a tradition and custom for marriage - and that's what's operative here. Same-Sex couples would have a status indistinguishable from different-sex marrieds. The custom of 'marriage' is determinative in this case.