Yeah, i'm not sure how you would monetize a place like 4chan. Most high paying ads would likely shun it like the plague, so as to not have their brands forever socially tainted.
pure speculation, but I'm pretty sure brands which are already socially tainted by the general public (e.g. adult entertainment) would gladly take up 4chan for ad space and visibility.
They tend to get similar advertisers to sites like the pirate bay. At one point, they had duckduckgo advertisements but I was so cynical that I assumed it was just crap like the rest of the ads... never clicked on it.
