It wouldn't need to be 10,000. We are not playing games there when MSG is available and we have a reasonable expectation of 10k or more attendance. We would probably want the on campus facility to be around 6,500 or 7,000, but comfortable.This is “just” a practice facility.
Imagine trying to build a 10,000 seat on campus arena. Thank God we have MSG because “ain’t gonna happen” is the name of our basketball arena fever dream.