Maybe. I’d to like to hear the argument Roberts et al use for that. It would take some contortions – not that they aren’t capable of that, but the Constitutional language is pretty clear that the states are in charge of their own elections, subject to the Voting Rights Act or other Congressional Act. Specifically, Article I, Section 4 states:
The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators (emphasis added).
I would note that some states (Georgia comes to mind) require a runoff if there is only a plurality in the first round of elections. RCV is not that far removed and, in fact, operates as an instant runoff. They could put in play their own schemes by overruling RCV.
To me the greater problem is the politics of state legislation, not the Supreme Court, but you could be right.