A relationship between Chrysler and Nissan already exists, with plans for Chrysler to port the Ram over for Nissan to rebadge as the next Titan, and a version of the Versa wearing Pentastar badging for the South American market is in the mix, so it's not like the two companies are strangers to each other. If Chrysler decides that it still wants its own platform, a partnership with another company to do the building might still be in the cards. Project D is about finding the most economic way to bring a competitive midsize sedan to market, including shrewd lash-ups.
According to Kicking Tires, Chrysler hopes to have a partner chosen by the end of the first half of 2009, with Nissan already being acknowledged as one of the possibilities.
[Source: Kicking Tires]