These guys send out millions of messages and they don't want bounces or flak. So they're never going to get any little auto-reply invoice. Minus that element, the proposal becomes simple spam filtering. Not too hard to do right now. Lots of people do it.
Spammers know people do it.
Tens of millions of spams go in the bit bucket unread. However, while it might create some interesting new markets, and perhaps change the direct-email strategies of some responsible companies, there's no way such a thing would make a dent in the daily flow of spam. A single idiot running an automated spam program can reach huge numbers of people. A dozen such idiots could probably annoy nearly every e-mail user on the planet. Therefore, you still need perfect filtering to keep out the idiots.