This prediction was inspired by Orin Kerr's observation:
O'Connor's retirement may shift the Court a lot less than people think. In the big ideological cases of the last Term, Justice Kennedy was the swing vote as often as (or maybe even more often than) Justice O'Connor. Let's assume for now that O'Connor is replaced by a consistently more conservative Justice; even if that's true, the left-of-center Justices presumably still have 4 very reliable votes and a good shot at picking up a 5th vote with Kennedy. Plus, new Justices are hard to predict, and it's often hard to tell whether a new Justice will vote consistently one way or another.