The other limitation is that ATC cannot see if there is an FMS vertical conditional limitation; take the DVR8M departure out of EGKK26L, there are three vertical requirements: Below 4000 @ 29DET, 5000 @ ACORN and 6000 @ 33DVR. With managed climb the final 'stop alt' of 6000 can be set and the auto flight will comply with the vertical constraints by going ALT CST*. I know airmanship, etc, may dictate that you don't trust the FMS vertical protection and incrementally set the altitude restrictions as you pass them, but after all, this is how the Airbus is designed. The problem is on Mode S, ATC has a canary when he sees the 6000 set on the FCU without being privy to the intermediate levels in the FMS route.