I also think a search engine like this would be quite hard to game. An ML-based classifier trained on thousands of text-heavy and media-heavy screenshots should be quite robust and I think would be very hard to evade, so the "game" will become more about how identify the crawler so you can serve it a high-ranking page while serving crap to the real users, and it seems fairly easily to defeat if the search engine does a second pass using residential proxies and standard browser user agents to detect this behavior (it could also threaten huge penalties like the entire domain being banned for a month to even deter attempts at this).