One important correction, Cameron:

Schulenberger argues that authors have little market power, because they have little choice on where to publish, and therefore an effective author-side market can not emerge.

This is incorrect. Shulenberger doesn't argue that authors would have "little market power" in an APC-dominated market; he argues (and this is a direct quote from his white paper) that a flip to APCs would result in a system in which authors have "zero market power." My argument, on the other hand, is that in an APC-based market authors would have sufficient market power to be able to make meaningful choices between publishing outlets. Shulenberger and I can't "both be right" on this point -- authors can't simultaneously have "zero market power" and some market power.

That being said--and to reiterate what I said at the end of my piece--none of this (in my case, anyway) amounts to an argument in favor of a flip to APCs. It's only a refutation of one particularly bad and poorly-informed argument against such a flip. As for the idea of a flip itself, I remain deeply ambivalent.