A better idea would be a generic content warning system replacing the existing NSFW toggle. This would not only improve compatibility with the rest of the fediverse (which does support CWs) but also give you way more filtering options than just "safe, tits or gore".
CWs should be applicable to both communities and individual posts, and would "stack" on top of each other. (Each post would "inherit" the CWs of it's community.)