>What's the difference between nsfw.youtube.com and pornhub?
There wouldn't be a difference. I would prefer only sfw stuff on YouTube and nsfw on other sites. If YouTube was required to host nsfw content I would prefer on a separate subdomain to make it easier to block.
>And youtube already hosts a lot of 18+ content, where you have to be signed in to see.
Correct. This is an existing issue today, however, since the nsfw content on YouTube is a bit more appropriate than a typical porn site so I am not as concerned. Watching a breast exam or something like that is a bit different than a gang bang.
I would like to see the existing nsfw content migrated off YouTube proper onto nsfw.youtube.com or something like that. It can be a challenge to actually block inappropriate content on YouTube. Allowing porn on YouTube would make it even harder.
(You technically can block nsfw content on YouTube already by creating a cname records in your dns server, but the average person can't really handle that)