Something like this. The Sierra Club is the primary proponent of this.
"The Sierra Club’s plans call for the recreation area to triple in size to more than 200,000 acres by connecting existing state preserve lands in New Jersey and Pennsylvania and unifying them under federal management. Some connecting private lands would be purchased as part of the upgraded designation."
I'll offer you a logical argument also as part of an answer. Why would New Jersey have to agree if the federal government already owned all of the land? If the state of New Jersey must agree for this to go forward, it would confer ownership of some type or form to the land, or some of the land, in question, or the NPS could just do what they wanted.
My point is that the implications things like this and the future plans of the entity wanting it are never clear, more often by design than not. And the farther the management of these gets from the state of NJ, the less input and weight that input has on it's uses. If the state controls that, os some of it now, why would anyone want to give that up?
Here is another favorite quote about this from the Sierra Club:
"John Kashwick, vice chairman of the New Jersey chapter of the Sierra Club, said upgrading the area to a park is a social equity issue and a way to make a national park accessible to underserved populations in New York City and Philadelphia"
That is a canard and is obvious, because it has nothing to do with the the preservation and management of that land or the other purported environmental goals. Social Equity. Right..........