This is just personal speculation, but I think the folks at Wingnut Wings operate under a few general "policies", for lack of a better term. First, and most important, would be what Sir Peter Jackson wants. It's his outfit, after all and he has a keen WWI interest.
Secondly, because he staffed the company with modelers and artists who are also passionate about WWI aircraft who want to design and produce accurate and faithful models of the machines that were flown in those days, the aircraft chosen to be made into models are personal choices, if not solely by Sir Peter, then surely he has the most influence on what gets done. And, being that faithfulness to the prototypes are paramount in conjunction with sane and reasonable assembly requirements for the modelers, I'd say their schedules of releases depend on it being ready when it's ready. Really ready for modelers, not because some previously set deadline dependent on purely financial requirements has been set.
Personally, there are enough WWI subjects on the German and Allied sides to keep all of us occupied throughout our productive modeling lives if all were to be finally kitted.
I think WWI is Wingnuts Wings forte and passion, and to stray from it would be disappointing and unnecessary. If there is a market for "inter-war" aircraft, surely another outfit will surface to feed it. I don't think the market is big enough for that however.
That said, I would again put forward my hope that the Fokkers F.1, Dr.1 and D.VIII will someday be produced by our Wingnut Wings nuts.