An interesting idea, but I would imagine that other faiths would feel discriminated against and they'd end up needing to appease each one by building their own religious buildings nearby. Besides which, as far as I'm aware the world trade centre was not a religious centre to begin with. While some may see the mosque as a symbol of the terrorists' 'victory', it cannot be a symbol of Islam's victory over Christianity or any other religion, and therefore building another religious building in between should not make any difference.
