Hi Edward,
In the old days I would have agreed, but in new resi wiring...not any more. The MWBC will not allow the CAFCI to function when both loads are operating. Even if the two BC's were not AFCI protected, there is a problem when the refer kicks in while the micro is running...and due to line coupling in the 3 wire NM cable feeding the SA, the device fault interrupter on the kitchen circuit will disconnect. Recently I replaced a GFCI on the counter that shared a micro and the kitchen SA#1 circuit. Both circuits were sharing the neutral when they were simultaneously activated. Seems the owner held the reset down on the GFCI while both appliances were operational. That fried the GFCI. What can be said about idiot proofing? Also note that MWBC's are obsolete in NM wiring if X10 or plc controls are added to shared BC functions. I hope this helps.