I don't understand why they're doing it in this manner. It would be easier for SCOTUS to just strike the marriage laws down and be done with it.
SCOTUS punted the ball with
Windsor because Kennedy was afraid the decision could end up being another
Roe. That is, a decision where the Court acted in the direction where public opinion seemed to be headed and in doing so stirred up a backlash that has served to undermine the credibility of the Court. So he went for a decision that would lead to that result in a more gradual fashion and thus give public opinion additional time to evolve before rendering a final verdict in a future case. Politically it made perfect sense and continues to do so. However, I think it made an utter mess of the balance that our Federal system should have between our cosovereign National and State governments in order to achieve the aim of rendering a decision that was politically more palatable.