I wouldn't count on any current race cars until their respective series are over. This includes the RJN Motorsport 370Z that took a class podium @ the 24 hours of Dubai.
There's the Bertone (BAT 21? or something) that won Pebble Beach. Dunno if it'll be ready for GT5 or 6, but expect that and the Camaro that won the award @ SEMA to show up someday. Also, we have the new Acura NSX concept to look forward to.