Making the case that his site condones and encourages pedophilia and posting of illicit material of children is trivially easy, and has been done to get him (unfortunately temporarily) kicked off of hosts before. The problem is actually connecting it to a real, specific human being for the authorities to go after. He needs to be linked to it in a way that's thorough, leaves no room for doubt, and is independently verifiable without having to blindly accept someone's word or blindly trust that a screenshot of a no-longer-available page was not edited or missing vital context. Otherwise, it's just hearsay and internet drama, because they have a strict standard of evidence that has to be met (imagine if some assmad redditor inspect element-ing a few screenshots was enough to get you arrested).
Reporting the site itself has been done, over and over, including by 4chan staff who have experience with NCMEC and federal authorities. NCMEC and the local authorities they contact (probably related to individual IPs making posts) haven't been able to get very far, since he's behind a tangled web of pseudonyms and proxies and infrastructure extending across multiple national borders, eclipsing the jurisdiction of any individual police department. The FBI would be the best bet, but one of the 4chan mods stated that the FBI has been completely ignoring their reports and that there's nothing more they can do if the feds aren't playing ball.
Maybe if enough noise was made about "a notorious pedophile spamming right wing sites with illegal material to try and get them taken down" and it reached the right politispergs online who had bigger audiences, it could reach the eyes it needed to, but I'm not holding my breath if the damn glowniggers don't want to do their fucking jobs. The ball's already in their court and they don't seem to be doing anything.
Daily reminder that every fed goes to hell when they die, no exceptions.