I still think that if there is a lot of office space created - in Manhattan, BK, Queens, wherever, it will be rented eventually. *With more office space, that more of a decrease in rents (most likely), which is what the city really needs to attract more business (and residents, for that matter).
Can you imagine the demand from the burbs, and all over America and the world (even in the city), if rents hovered near $20-$30/sq. ft.? *
It may reduce the developers profits, but they may be able to make it up in volume.