At page 17 of the revised version of his essay, he writes:
For if Amazon, Microsoft, or any Google rival does in the future offer any books for new sale that are not derived from the Google scanning project, then (even if those books are currently out-of-print) those books will become “commercially available,” and then the settlement will by default exclude them from sale via Google. The settlement thus by definition does not give Google any default license or plausible de facto monopoly over any books that any rival would offer in the but-for world.
This is not a conclusive argument. For one thing, the heart of the antitrust issues have always been horizontal agreement among copyright owners and and illegitimately acquired exclusive access to unclaimed works, neither of which is quite at stake in this part of the discussion. But it is still a powerful, subtle point, worth reflecting on.