All of the main servers I've seen have a no porn rule. I suppose it's only a matter of time until someone's willing to stand up their own Lemmy porn server and take on the responsibility of moderating that.
I suggested to PornHub that they should host their own lemmy instance for porn. It's stuck in limbo though awaiting mod approval.
Edit: I'm curious, I see I've gotten two downvotes, can someone who downvoted provide a reason why? Just anti-porn sentiment? Do you not want porn on lemmy? Don't like the company PornHub? Think it's a stupid idea for some reason? I'm serious, I'd like to know why you seem to disagree with the suggestion that PornHub should host a lemmy instance explicitly to post porn on. It's entirely possible I'm missing something here.
That is actually great idea, some organization hosting lemmy instance concerning their work.
Like Debian hosting free software lemmy communities, some marketing agency hosting design and creative communities. That way instances can ve snallee and manageable.
Of course it needs to get a bit more obvious how to use different instances.