It takes 4 justices to call up a case and the Roberts court is trying to avoid partisan cases leading into 2020. Best course of action and what I believe they are doing is letting the appellate process play out, I think that’s the most prudent approach and delaying taking action on a contentious issue.
I think they’re watching closely at the circuit courts hence the conferences on DACA. I’m really hoping they see the Administrative Procedure Act as a constitutional power by congress. Otherwise, the regulation and rule making process of the executive branch will become presidential law making