I think the next sequel will be Western Front, there are more American and British planes in FB than in IL-2 and there is even an American mission.

The reason I think there will be another sequel is the complete American pilot voices. You don't create complete series of voices (there is as much variety in phrases as the Russian and German ones) for the sake of ONE MISSION.

so either there'll be a patch with more US missions, or another expansion is on the horizon.