> If this "replacement" ever did, theoretically, been seen as suitable, all that would happen would be that attack code would suddenly see an increase in quality.

This is where I believe security-through-obscurity is underrated. As long as you're small enough that targeted attacks aren't part of your threat model, merely being unique affords a great deal of safety. Your wierdo jerry-rigged authentication system may not be particularly robust, but it's more likely than any mainstream product to repel an automated attack.