Maybe the CFS series isn't very interesting for Microsoft to do. If you look at the NAme Combat Flightsimulator alone I see some problems. As Hagar said a part of Flightsim folks will look down on it because they think it's Just a game.  Now there are Gamers/People who don't want a Simulator. They want a game. They might think that CFS is too much fiddling with the planes and Too little action in Flying. We all know that that isn't so but they don't And If the Flightsim folks look down on it and the regular folks don't want a sim......Then who is left to buy it? + For the flightsim folks that DO buy the game..They expect Compatability with Flightsim itself and stuff like that. If Microsoft would launch a entirely different  Flight/Combat game you would have less people expecting it to be compatible with fs and all that stuff. + people looking for a flying game will buy it quicker. So maybe that is what Microsoft will do. Launch a game under an entirely different title, completely different from FS itself.

But that is just a guess. They might Buy a developer like Ubisoft and Launch such titles under their names.

Just all guesswork

Its sad there will be no CFS4.  IL2:FB is fun but it lacks the atmosphere cfs3 has. When I fly cfs3 I can get a feeling I am in the war, IL2 dose not have that element for me. Don't know why no one likes the cfs3 engine, people say it is riddled with bugs but I cant say I know of one, but im not lookin either...