Codemasters has revealed that although they are aware of fans wish to have GP2 in F1 games it is just not possible at the moment due to the license if currently has for the sport.
Although if they were able to do it, it would not be a standalone game and would be added as DLC.
Chief Game Designer Stephen Hood told Thunderbolt;
At the moment this is not possible because the license does not allow us to include GP2 even if we wanted to (plus we would need a much bigger team),
Maybe in the future this is something that will change. I cant see it becoming a standalone game but it would certainly make for interesting downloadable content one day.