One of the intriguing things about Google's test of a mutant CPM model and new site targeting features is that it is an actual beta! In other words, they are announcing the details in advance, while a small number of users get to test the new features.
Why would Google do it that way? Usually, they get it ready and then spring it on the world and call it a beta for the next several years. Pre-announcing is not really their style. Maybe they are starting to eye Yahoo's more diverse piece of the ad world pie. If that is the case, they're sending a message with this beta.
Additionally, by pre-announcing, Google is giving time for all the media planners and buyers to include them in their summer campaigns.