I think this is one thing where the relays need to do the filtering and just assume they're gonna get sent absolutely everything.
To take an example - successful OnlyFans models are good at marketing. When they hear about "blaster relays" that rebroadcast to the top 100 relays they're gonna be all over that. Being professionals you might get them to hit a classification button (G, PG, R, X type of thing) before posting. That could warn the relay of what's in the content, but they absolutely will try to get as much reach on every post as they can. OnlyFans might be where they make the sale, but it's not where people hear about them. Getting as much reach as possible is literally dollars in their pocket.
Then there's Joe Schmoe who just really likes sharing explicit content for whatever (non-commercial) reason. I don't think you'll ever get guys like him to label their content - he's not a professional - not even a pretend professional.
Bottom line - if you're expecting people to send different types of content via different relays - that effort would be better put towards having them classify the content before sending since they're literally classifying it (at least mentally) to figure out which relays to send to.
So far the only Nostr client I've seen that does a decent job allowing you to switch between accounts is Hamstr.to - and I'm not sure it's status - if I'm looking at the correct GitHub page - it hasn't had any activity in 2+ months. So you can't really tell people to have multiple accounts if the clients can't handle it. Plus - some people just won't have multiple accounts. I'm sometimes shocked at what my younger friends mix on a single social media account.