> I don't know if many researchers, for example, who usually know their field quite well, would be willing to volunteer their skills.

They already do, when they referee papers. Journal peer review is unpaid. This text-reviewing idea could find its way into the system as something similar. Especially since the reviewers might have a better incentive. Journal peer review helps fellow researchers. But if I'm planning on using a text, then helping to review it helps me -- and my students.