This is from 2006. I don't fully understand it but it looked interesting. Something I've never seen discussed before. It did seem at the time that the whole amendment thing was dropped rather as quickly as it started. In-house law staff: Could this have been a contributing factor to that?

http://repository.law.miami.edu/cgi/viewcontent.cgi?article=1331&context=umlr
...A same-sex marriage amendment, tribal nonconformance, and the federal or state response to tribal nonconformity could generate yet another constitutional crisis in federal Indian law....

...Indian tribes are part of Our Federalism one way or the other. A same-sex marriage amendment might bring incorporation of Indian tribes into the Constitution to the forefront because domestic relations, the particular subject matter of the amendment, would create an unexpected constitutional crisis. For Indian tribes seeking entry into the constitutional structure (and not all tribes do), the crisis would be more of an opportunity. But for the Court, struggling to balance its federalism jurisprudence between just two sovereigns, 39 the addition of Indian tribes as a third constitutional sovereign may force it to push the reset button on federal Indian law...

...A constitutional amendment prohibiting or authorizing same-sex marriage in the United States and its territories - and including Indian Country - could have the concomitant impact of creating implicit recognition of modem Indian tribes in the Constitution and Our Federalism....


http://www.law.msu.edu/faculty_staff/profile.php?prof=494
Matthew L.M. Fletcher is Professor of Law at Michigan State University College of Law and Director of the Indigenous Law and Policy Center. He is a member of the Grand Traverse Band of Ottawa and Chippewa Indians, located in Peshawbestown, Michigan. He is the Reporter for the American Law Institute’s Restatement, Third, The Law of American Indians. He sits as the Chief Justice of the Poarch Band of Creek Indians Supreme Court and also sits as an appellate judge for the Grand Traverse Band, the Hoopa Valley Tribe, the Lower Elwha Tribe, the Nottawaseppi Huron Band of Potawatomi Indians, the Pokagon Band of Potawatomi Indians, and the Santee Sioux Tribe of Nebraska.