I would agree. There’s a full plate as it is right now.
The curious thing here...you can’t identify anything in the Constitution where Congress can manage or control marriage...except for possible the commerce clause (that’s the one that health care fell under). I suspect that they will say that the national government can’t regulate, award, or control marriage...with the current Constitution. So it may invite lots of lawsuits over how taxes are done, or how benefits are done via social security.
However, they may point out that several states have Constitutions which discuss this, and they are within their limits of making various laws to manage marriage. So a state-by-state effort will come out of this.
I think the primary argument would come from Article 4 Section 1:
Full faith and credit shall be given in each state to the public acts, records, and judicial proceedings of every other state. And the Congress may by general laws prescribe the manner in which such acts, records, and proceedings shall be proved, and the effect thereof.
But then you have medical licenses and bar admissions...neither of which is recognized across state lins. And the state licenses marriages...they are not strictly a private contract between two (or more) people.