Hi
Since the FPU is an option in the Cortex M4 core it will not affect the pin out of the parts so I don't expect that there will be a difference due to this.
However I would contact your freescale representative about details of which parts will be offered with the FPU. I understand that the K70 will be the first part (in the next month or two) but it may be that the option will be restricted to the larger, higher speed parts and not be available for the K20 (I don't expect that there are plans for offering it in the K20 so you need to make sure before defining it for project use).
Regards
Mark