It would make a good second (or third) layer of defense. The problem with it is that it's reactive not proactive, so you need to download the ad first before it can decide to block it or not. URL blacklists are the superior option, but hard to maintain. The ideal setup would be a URL blacklist that's automatically updated on the fly by an AI classifier so anything that slips through the blacklist gets ban hammered by the AI and added to the blacklist to prevent future wasted bandwidth. If the blacklist updates were shared the same way some of the ad blockers do currently it could be incredibly effective as it would be essentially distributed realtime ad blocking.