The type of accessibility being discussed is that of "the degree to which the scholarly content itself can actually be understood by the generalist reader." A piece of work might be more or less accessible for a number of reasons, including the quality of the writing, the use of subject-specific jargon, the use of formats inaccessible to people with disabilities, the inherent complexity of the material, and the inherent coherence of the writing itself. The author's main point is that "Not all complexity can be reduced to simplicity without a real sacrifice of meaning." That's probably true. But it's not an either-or proposition. I think all audiences can understand anything to a certain degree. The purpose of quality writing is to extend that degree to the greatest extent possible.