They're also adding MHL compatibility for cell phones and tablets.
Picture-in-picture isn't a new feature in and of itself. It's something that's been offered for a while and it makes TV viewing a much improved experience for some folks. Onkyo's new receivers will be offering something similar but much more interesting.
With their 2012 line of receivers you'll be able to use a feature called InstaPrevue to bring up a picture-in-picture view of any of your HDMI or MHL inputs. It's a nice addition that will certainly have a few really worthwhile uses.
The other new addition to Onkyo's receivers is MHL compatibility. MHL is the high def output used most often with phones and tablets and usually requires a converter to get to your TV.