(Pax speaking) With such a crucial moment as mode change, might the a/c not 'call out' itself? In the same way that it calls out other critical things to do with GPWS, height calls and 'Retard' - it could call the change and require action by the crew to ack?
I appreciate that there are many, many indicators and call outs on the flight deck but such a critical change might deserve it's own.