The Supreme Court has granted cert. in Town of Greece v. Galloway, a case out of New York in which the Second Circuit held in an opinion by Judge Guido Calabresi that the town’s practice of allowing volunteer private citizens to open town board meetings with a prayer violated the Establishment Clause. The last Supreme Court decision to address this precise issue was Marsh v. Chambers (1983), where the Court in a majority decision by Chief Justice Burger upheld the particular practice at issue in Nebraska. Courts of appeals have taken different approaches to the issue post-Marsh, even within the same circuit (see, e.g., the Fourth Circuit’s very different approaches in Joyner v. Forsyth County, Wynne v. Town of Great Falls, and Simpson v. Chesterfield County) so I suppose it was on the Court’s radar. But one never knows exactly why the Court decides to take up an issue.
For some discussion of the Second Circuit decision, see this post.