aggressive preprocessing is the secret, because most errors can be located automatically, so the pages are clean before they even get to "proofers", who are really "smoothreaders".
Agreed with this part at least -- many motivated "early readers" love a particular author, and would be happy to get early access to the text via some kind of tool that allowed them to fix or at least mark the bugs they find as a part of their reading. "Marking" bugs as a part of reading could be as simple as asking them to read on a notepad or what have you and put a Q-mark in the text where they think they see a bug. Then diff their back submission to find the bugs that need to be fixed. Readers of e-books could even back-submit a "bookmarks" file that tags where errors were seen allowing proofing to be done on any e-book reader.