There are some big problems with this, mostly that openAI doesn't want to break even or be profitable, their entire setup is based on being wildly so. Building a Google sized business on ads is incredibly difficult. They need to be so much better than the competition that we have no choice but to use them, and that's not the case any more. More minor but still a major issue is the underlying IP rights. As users mature they will increasingly look for citations from LLMs, and if open AI is monetizing in this vein everyone is going to come for a piece.
