I don't fly Airbus, but the thing with mode callouts is if you don't notice the mode change, you won't call it (obviously). It is most useful, in my opinion, when making mode changes as it forces you, or should force you, to look at the PFD or whatever your modes are annunciated on, and confirm the change then call it. But if a mode has changed automatically and neither pilot realises, then mode change callout SOPs won't help. In other words, it works as long as at least one pilot is "in the loop" and it helps bring the other pilot into the loop.