Our sharp-eyed Controller brought this piece at Bnet to my attention. Google has filed a patent application on a technology that would allow display ads to be fired in response to a user search.
From the description here, it sounds like this may be less about replacing text ads with display ads on the SERPs and more about providing additional detail on the advertiser's offerings without leaving Google. Perhaps like Google Image Search, where hovering over the image gets an expanded image, perhaps the notion would be hovering over the text ad, would get a more detailed list of products/product categories/features/price lists, etc.
Perhaps this would be more tied to the Product Listing Ads than core AdWords search which typically involves somewhat murkier user intent, making it more complicated to provide such details.
Sheer speculation, of course.
The idea of replacing the static text ads with a potentially more engaging, rich media experience has been kicking around for a while. Perhaps this is the sign that Google is indeed moving in that direction.