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.