It looks like the NEC never anticipated unavailability of dual function circuit breakers for MWBCs.
While 406.4(D)(3) addresses replacement of receptacles requiring GFCI, there is no mention of updating hardwired appliances or of replacement of circuit breakers.
I think this means it's simply not feasible to add GFCI protection in this situation without modifying the dishwasher circuit. So replacing the old circuit breakers with a 2-pole AFCI seems reasonable.