If the client UI makes it easy and clear to set a topic, those people who care about posting high signal content to their diverse audiences will definitely not forget - and those are only the people really worth following anyways. Don't care if someone abuses it to spam - I would simply unfollow them.
You’d have to more many people. This would get abused for sure.
But yeah some clients could add tagging like snort used to have.
Not sure if I get your point. Why would I have to mute many people? You think they would setup a topic "Programming" on their profile, but then post politics all the time and tag it either as "all" or "programming" and then I would get to see their politics takes even though I only followed their programming topic?