ProBlogger is reporting a lot of AdSense publishers noticing that Google is offering them the ability to place video content from YouTube on their sites, which will display video ads within the ads.
There is a corresponding thread at DigitalPoint Forums which provides more support for the story. Reportedly, there is a URL that works from some AdSense Publishers that allow them to sign up for this beta. The URL is https://www.youtube.com/signup?next=/adsense_learn. For me, that URL just takes me to the login page and after I login, it doesn't do anything.
The page reads in part:
Enhance your site with high quality, relevant video content from YouTube partners, and earn extra revenue along the way
Forum discussion at DigitalPoint Forums.