It makes no sense in North Philly by any metric. There's no location there that's as accessible to the entire region as Market East, that has every rail line as a one seat ride, that has the highway access, the parking garages, or that has the existing entertainment service infrastructure to support it.

The only locations that make sense are Market East, the Stadium Complex, or Camden. The Sixers want a downtown transit oriented building, the bankrupt mall owners want to downsize the property, and the city wants Market East to develop more; which is why building on top of Market East Station makes perfect sense.