Not to be overly cynical, but this seems like it's the likely outcome in the medium-term.

Billions of dollars worth of data and manhours could only be justified for something that could turn a profit, and the obvious way an advertising company like Google could make money off a prompt handler like this would be "sponsored" prompts. (i.e. if I ask for images of Ben Franklin and Coke was bidding, then here's Ben Franklin drinking a refreshing diet coke)