CFS is not pay-to-play on the Zone.
FA and CS are not WBIII. While there may be player crossover, they are not the same games -- they cater to different crowds (FM, strategy, dare I say arcade).
MS may look at it as another monthly-fee money making venture. Let's face it, WB has an existing customer base, so the only drop-off you'd have is people who hate MS or possible server problems after a move (not to mention MAC users). They could be reasonably sure that there would be a base from day 1.
VR-1, a third party company, developed FA for MS (third party until MS bought a stake in them). No reason to believe that MS could not do the same with WarBirds.
Fury
speculation only