Ryan Davis said on one of the recent Giant Bombcasts that Bizarre had kept the IP and kept it purposefully on the down low... maybe I misheard it? Maybe HE misheard it. D:
I hope if there is a PGR5 it is done right. PGR4 was one of the most stylistic racers in presentation and had a legendary (electronic portion of it) soundtrack. The visuals and rain/snow effects were also very clean and shockingly amazing for the time, and even still.
Fairly dubious about this rumour but if it is true then it's for the next generation. MS aren't going to invest in such a packed genre at this point of the 360's life but they could be making sure they've got the staples covered for launch with a flashy and accessible title.
Edit: Just realised this was from Develop & is therefore most probably true.