I think that would be useful! I also think that anyone putting that much work in should look into hosting their own server, because they've already done the hardest part of hosting a server in the fediverse. A big part of the issue is that a lot of ActivityPub apps don't really have granular enough customization baked in to support that sort of thing just yet; you can get some apps that do that on the user side, but anything on the server/community side is usually just "block all" or nothing. The admin of my Mastodon instance is always complaining that he can't just hide certain instances from the "all" tab without blocking then entirely, and he just wants to hide them so they don't overwhelm the server, not block them from showing up for people who choose to interact with them.