The idea that we're experimenting with in Matrix is instead to let anyone publish a reputation list (greylist), and mix together existing ones, and use it to apply whatever rules they like at whatever granularity they like. In other words: at the account level, let users hide users or rooms they dislike. Or at a community level, let moderators block users based on whatever criteria. Or, worst case, at a server level (although we haven't seen much of that in practice, unlike email or activitypub).

For instance, an obvious capability would be for rep lists to also have rep themselves, so you can gauge whether a given rep source has become corrupted, and switch as needed.

In other words: this is primarily about empowering users, rather than empowering admins, and giving users the tools to block stuff on their own terms and make up their own choices, rather than being beholden to a DNSBL-style cabal, or whatever rules their server admin happens to adhere to.