I think a MWBC feeding a circuit of receptacles that are required to be GFCI protected is one time a MWBC will always have a common trip if a GFCI breaker is going to be used, personally I don't like using GFCI breakers when a GFCI receptacle can be used, for one it is much nicer not to have to go find a breaker panel to reset it.
The only thing I can say about only using 2 20 amp circuits is this customer is not going to be a happy camper when they realize how many times they are going to trip the breaker, most of my kitchens will have at least 6-9 20 amp circuits, and if a counter is large enough to have over 4 receptacle openings, it will get another 20 amp circuit and GFCI receptacle, Never short change a kitchen, if you want happy and customers will want to use you again, don't do it.
I think the worst thing to happen is having breakers start blowing right after a homeowner who probably had this problem with their old home, goes through all the trouble of building a new dream home, and goes through this again, if it were me, I would blow a cork.
There is no way just two receptacle circuits would not trip with all the high wattage appliances we have today.
Now there is just no getting around a George Forman Grill, even with all the circuits I install they will still trip it, those need to be on there own circuit lol.
