According to the Atlantic Yards Modified General Project Plan (p. 22):
ESDC's acquisition of all such properties [via eminent domain] will not occur until such time as ESDC receives commitments, guaranties and other evidence satisfactory to ESDC that FCRC will (i) promptly commence construction of the Arena, the Upgraded Yard and all of the infrastructure necessary for the Arena (collectively, the "Arena Infrastructure"; together with the Arena and the Upgraded Yard, the "Initial Development"), and (ii) complete such construction within agreed-upon time periods.
If developer Forest City Ratner does not create the upgraded railyard it intended--as the New York Times reported, citing an anonymous source--would that be violating the General Project Plan?
Then again, there's often some wiggle room. It probably depends on the definition of "Upgraded." But the issue is worth tracking.