Sony has confirmed that the new upcoming handheld (or NGP, if you prefer) will offer backward compatibility.
While the backward compatibility offering may not be ready on release day, the unit will be able to play downloaded PSP titles that users already own. This news is actually a bit of a surprise, considering that the last time Sony did backward compatibility (as on the PS3) they ended up tossing it out.
From what we understand, the backward compatibility is really nothing more than downloading a new NGP version of the game. The NGP updated versions will offer some additional support, such as support for the second analog stick, for example.
Rumors of cross platform play continue, but we will see how that evolves the closer we get to the actual E3 announcement. According to the whispers that we have heard, Sony plans to launch the NGP in at least one region during the holiday season. If not by the holiday season, it will be by the end of the year, for sure. It is likely that the NGP will not arrive in the U.S. until at least next year.