Yesterday's order from the Supreme Court can be found here. It was a 5-4 decision, breaking down on the usual lines, with Sotomayor, Kagan, Ginsburg, and Breyer in dissent.
This does not prevent any state from continuing to work on its implementation plans, and we certainly hope Minnesota does not slow down its efforts. The EPA will not be able to order states to do anything or impose any federal plan on them until after the Supreme Court has decided the case.
The DC Circuit Court of Appeals has the case on an expedited schedule, so it will be briefed and argued this spring and summer, and likely decided by the end of the year. The Supreme Court can then take the case up in its next Term, but would likely not decide it until early summer 2017.
It's a bad decision (see comments from California AG Kamala Harris), but it does not at all mean the rules are doomed. I think the EPA is on a solid legal footing, and even this Court has been generally upholding Clean Air Act decisions. It is not news that five members of the Court likely don't care for this rule (or very many environmental rules) but that does not mean one or two of those five won't vote to uphold it. As I've written about previously, the statutory interpretation argument the opponents are making is a lot like the argument about the state vs. federal health insurance exchanges that the Court, and Chief Justice Roberts, rejected just last year.