I don't see this catching on. The thing that makes latte art interesting is precisely that it's hard. No one looks at the cover of an O'Reilly book and says, "That's amazing!" But if someone handed you a sheet of paper on which they had drawn an animal that looked just as realistic as an O'Reilly cover, you might very well say that.
I might actually be willing to pay an extra 50 cents to NOT have an ad printed on my latte, not to mention the extra time to print the ad while my coffee gets cold.