I'll just add a bit more as another thought occurred to me.

Part of this rumour included a rumour that the WW1 game was having trouble in development and may be delayed indefinitely and the reason given was the difficulty in creating a new engine. I initially did not think much of this given that 40k and Starwars would need the new(they say that it's new but I would assume it's actually just updated) engine as well, so either they would all be having issues or none of them would.
But then it occurred to me that while yes, that's true form a tactical battle sense, the strategic maps would probably be quite different as WW1 revolve around front lines and not traditional armies like in Total war games, that's probably where they are having the difficulty. That could be a bother.