Plus, a good point that was brought up today at the trial I was at. What if your "mixed breed" isn't a mixed breed at all, but instead is a very nice show/working dog of a non-AKC breed. Still can't compete it at the AKC shows, because you would have to s/n to do so. So you've knocked that segment of the dog world out of your money-making scheme. In fact, it makes me wonder if you can register a purebred of a non-AKC breed at all? I mean, I guess you could just lie and say it's a mixed breed, but is that going against the purpose of the rule.
Honestly, I've talked to a lot of agility people in the last week between classes, run-thrus, and the trial, and I have yet to hear one say "Great job, AKC!" no matter if they are pro-AKC/purebreds or mutt fans. This isn't just a case of not being able to please everyone - they appear to not be pleasing ANYONE.