I saw somewhere some WWI planes in the works for an Oleg style graphics engine (I say that, because they were rumored for FB, but I'm not sure about that... Oleg is supposedly definitely making a game after FB... theater/era unknown... reportedly one of the reasons UBI started the Strategic Simulations line of software). This forum here will show you some of the projects in the works for:
http://www.il2center.com/Forums/viewforum.php?f=22 It won't be a full fledged WWI product, but will give planes of the same years that match up in performance for Germany and Britain (France too I suppose, but I haven't seen any Nieuports or Moranes).
Off topic: There's also a Luft '46 project in the works for, I think, FB... so far the game already includes the Me262, will later include the He-162 as flyable, and the Me163. There's also a P80 and Horten Go229 in development, the former to be released for FB in a later patch... unsure about the latter.
-SW