I like the idea, but does it come with a default list? I'd be interested in something like this but that includes most known blogspam sites, with a global list like say pihole provides.
Given the nature of domain-level spam, tuning your own list is likely to be both fairly quick and effective.
High-ranking search results don't come easily, and there will be a relatively small set of domains occupying any such slots. Even with turnover, that's going to be viable. Remember, the competition here isn't to flood your inbox from any random domain on the Net, but to secure one of the first 10 SERP results. Odds are good that blocking 10--20 domains will be more than enough.
Your list will also likely vary from other people's.
I don't think it works at the provider level - one person's junk is another person's treasure, and there's always going to be content that could swing one way or the other.
