Most trolling and brigading is fairly low effort, and having a sharable collection of communities to troll makes it much easier to organize lots of people to do just that. Edit: yes external tools for that exist but having it built in makes it much easier to abuse and rope in people to do the trolling that otherwise would not bother.
But my main concern is that this isn’t opt-in for communities. Having a sharable and subscribable link with for example “meme” communities means that all of them are seeing a constant barrage of random people commenting that are not members of that community and do not have any idea what the community is about other than that it is somewhat loosely related to “memes”. It basically hides everything that is vital about the communities and actively damages attempts at community building.
Will there be a way for communities to opt-out from being listed in a category?
I think there is a lot of abuse potential in this and even if well intended, a single word or so can’t really describe what communities are about, and as a result those categories (similar to the “all” feed) will bring a lot of off-topic comments and trolling from people not engaged with the communities at all otherwise.
On Mastodon with hashtags the original poster can at least make a conscious choice of being listed under it or not. But this seems fully third party driven and I fear it will increase moderation workload significantly.