Fwiw, PieFed does that already. It’s still working on the foundationals, but it already has features like Categories of Communities, hashtags, the ability to block all users from a user-specified instance, a separate NSFW vs. NSFL/gore, and more.

So when you join you choose the “Topic” areas that you are interested in, which populates the Categories/Topic areas, i.e. you opt-in. Though tbf the flagship instance PieFed.social has defederated entirely from hexbear.net and lemmygrad.ml so there’s a difference between “PieFed” the Lemmy software replacement and specific instances, ofc, the same as in Lemmy.

Some high-functioning apps let you do a bunch of this as well.

Also PieFed allows the admin to add “labels” to places, like this one appears on every post from Beehaw:

This post is hosted on beehaw.org which has higher standards of behaviour than most places. Be nice.

With that link going to their very own statement of purpose, in their very own words, rather than having other words forced upon them. So friendly!! (See example of it in action here, and while I am at it, another example, this one showing off Communities at the top and hashtags at the bottom of the post, plus as you scroll past the comments you see the “sidebar” text below every single post.)

Also there are labels for users too - like one for brand-new accounts, another for people who receive significantly more downvotes than upvotes, and so on. You could be scrolling through a post and see a tankie user account with the label next to it, but decide for yourself if you want to engage or not. It is a helpful little warning though that by doing so you would be engaging with someone known to be an extremely low-reputation troll.

Lastly there’s a bunch of features that allow for what I’ll call “democratization of moderation”, where instead of a moderator making allow vs. remove binary decisions that affect everyone in a community equally, each end user can make their own thresholds to decide what level of contentious behavior to show or not. PieFed will auto-collapase or even outright auto-hide posts that receive a certain large number of downvotes, or just set the threshold super high to disable that feature entirely (as I did). I find that neat though bc no longer will it be the case that someone else’s freedom to speak becomes my freedom to have to listen, despite my lack of consent, and it wouldn’t even require a mod to remove content, just some time for a community to do its voting procedure as normal.

So I eagerly look forward to when PieFed becomes more developed! I’m already using it as my daily driver, although tbf I can’t recommend it to someone brand-new who doesn’t have a Lemmy alt to fall back onto when encountering scenarios that PieFed does not handle well yet, like searching for posts.