News: Apparently it is.
French car manufacturer Peugeot has subtly let the cat out of the bag concerning Project Gotham Racing 4. The company is currently running a concept car design contest and one of the honors the winning design will receive is being included in the aforementioned PGR4:
"In addition, the winning concept car will be included by Microsoft in the Project Gotham Racing 4 game, exclusively on Xbox 360 that will be released towards the end of 2007 or first half of 2008."
So there you have it. PGR4 is coming in either late 2007 (maybe) or early 2008 (more likely). And while it's a little unconventional to announce the title on the contest page of Peugeot, no one should be surprised a sequel to one of the 360's biggest launch titles is on the way.
We'll have more on the game when it becomes truly official.