It has to be much more appealing than that, and with data to back up the big promises. That's where email marketers can really benefit from this concept, particularly those with 20,000+ strong subscriber lists. Offering a sponsor exposure to a whole new audience through three or four of your upcoming email blasts plus their logo listed in your book's front matter, in exchange for them paying you upfront to write your next e-book, is a much more enticing offer. And it will work even better if the content of your new e-book matches one of their products or services really well.
Here's a perfect example: Google "Al Pitampalli" and "Citrix Systems" for more details. In a nutshell, Al got Citrix to sponsor his book titled Read This Before Our Next Meeting which is a perfect fit considering Citrix invented GoToMeeting videoconferencing. They were able to cross market to each other's followers and both benefited greatly from the partnership.
I can see this working well for non-fiction books. Not sure about fictional books, though. Your thoughts?