I am interested to see if they are now using the retina graphics of iPhone apps if they have them when viewing on the new iPad at 2x mode or are still using the 360x480 version now at 4x?? Shame that RetinaPad hasn't become a standard feature of iOS even on the older iPads.
Chances are the iPhone only apps on the retina iPad will display as the retina version of the iPhone app.
I'm guessing you will see 1x and 2x versions using the Retina resources. Continuing to scale up the non-retina versions of iPhone apps would be pretty silly at this point.