Marriages began in Utah because the state had not asked for a pre-emptive stay (in the event they lost the case in district court, as they did). This may be because of turmoil in the attorney general's office.
By comparison, when District Judge Vaughn Walker found that CA Prop8 was unconstitutional under federal law, he immediately stayed his decision, before appeal to the 9th circuit even happened. That's because the guys on the other side filed pre-emptively for a stay pending appeal. This led to years of further delay before SCOTUS eventually allowed the decision to stand.
There is also some discussion on whether the marriages that have already occurred in Utah (over 1000, I've read) will remain legal.
In California, during the window prior to passage of Prop8 in Nov. 2008, about 18,000 of us married. It wasn't until June of that year that the state court agreed that those marriages remained legal, because they had been legal under state law when they were entered into. And the fact of their legality, leading to some gay people who were married, and some who couldn't, was part of the federal court case that eventually led to overturning Prop8.
(Contrast this to the marriages in San Francisco a few years earlier, which were annulled because they were illegal under state law when performed by rogue SF mayor Gavin Newsome).
My bet is that the marriages currently existing will stay legal, because they were legal when contracted.
But we'll see.
Meanwhile, Utah's argument continues to be based on procreation and child-rearing. But the case has nothing to do with adoption, only with marriage. And given that many gay couples are already raising kids, and legal marriage will not change that (although it will provide benefits), that argument, which is the primary argument of most of our opponents, would seem to be a non-starter.
I have mixed feelings about this. I fear, along with Justice Ginsburg, a Roe-v-Wade backlash if SCOTUS goes big. OTOH, they can also punt. Even if the 10th circuit finds for equality, if they find narrowly enough that it only applies to Utah, there's no requirement for SCOTUS to take the inevitable appeal.
Again, we'll see.