Pier 5 will never be converted - it is a community park asset.No idea if it's technically feasible, but as far as Brooklyn options go, Pier 5 would be great as far as accessibility.
I wrote a while back pontificating the possibility of CFG buying/leasing 1-2 piers at the adjacent NYNJ Port Authority Container Terminal and building there as it has easy access to the BQE, nearby subways, and a mile from the Atlantic Terminal. This would be a more likely option than taking highly used park space from the Brooklyn Bridge Park.