[GeeTwo]

The biggest change to the control board would be to reflect that the four wheels must be independently driven. As such, a minimum of four motor controllers is required. If you put encoders on your wheels, you will need four, not just two. Quadrature encoders would require eight channels on the DIO, unless you're feeding back directly to the controller (e.g. Talon SRX).

Many teams which do mecanum also like to use "field coordinates" which allows the robot to go the same direction as you push the joystick, even if the robot is sideways or backwards. This will require an analog gyroscope to use the libraries.

If you only use pneumatics for shifting, this may go away; few team shift mecanum (apart from octanum style "shifting").