True, but also being a bit more random where it's not trivial to filter the bot on the spammers side would make it just a little bit harder to ignore.
While I think the donating of DNS records is an interesting idea, I personally wouldn't want to risk giving permission to an outside party for the domains I use, and I don't think it would be worthwhile to try and correctly maintain a domain just as a donation.
I already support several projects like this.