Was just running through the first installment of the "Optimizing Adsense" course material released today and see that two new types of ads are on the horizon.
1. CPE (cost per engagement)
2. Active View CMP
Active view ads mean that at least 50% of the ad needs to be viewable on-screen for at least one second and CPE stands for Cost Per Engagement.
I've been wondering if CPE's would ever make an appearance so there, apparently, is the answer. This will certainly give publishers a few things to think about. Anyway, absent a complete analysis of the future, I guess we'll see what we shall see.