You mean that the new development plan includes the spatial boundaries of the neighboring development plan and effectively creates a new one out of two old ones (?)
Not quite. Like wpic, I assume that it is an old development plan (maybe from the 1960s). If the new development plan partially supersedes the old one, that would be an indication that the city planners have realized that the legally binding old development plan no longer meets today's requirements, but they shy away from the effort of a complete repeal procedure. However, if new desires regarding the remaining scope penetrate the city planners, there would be the slight hope that the entire plan will still be repealed or superseded. All wild speculation. I just want to express that I do not share wpic's optimism but there could still be local constellations that might make the desired development possible after all. Perhaps a local architect indeed has a good connection to the authority and makes dreams come true.