No the stadium will be built on the current parking lot of Citifield since that is NOT parkland so you won't need approval to build a stadium. The willets point are will be built with additional parking, shopping , housing whatever else they decide. Hopefully it will happen but knowing who things work in NYC who knows.
The parking lot *is* classified as parkland. The state approved Shea Stadium and ancillary structures to be built on that land, such as the parking lot. A mall and another stadium are not ancillary structures to a baseball stadium.