@wayneosdias the 4Hz sampling rate only applies to the rate at which data from sensors (configured using M307) is collected and returned from the expansion board to the main board; and to the collection of data from sensors connected to the main board into the object model. The actual sampling in the ADC is much faster on both main boards and expansion boards. Changes to digital inputs are also signalled from expansion boards to the main board very quickly. Likewise when an analog input configures as general purpose input crosses the threshold value.
So it's entirely possible to do the processing you want on your custom expansion board and pass it back to the main board over CAN.
OTOH if you need the data to be passed directly into the Pi (or other computer running OpenPnP) then that would be a reason for bypassing the expansion board processor and CAN and using a separate cable back to the Pi.