I fly for a major European Carrier but operate out of one of our smaller bases and as such have known most of our Cabin Crew for some time. As Captain, I will liase with the most senior member of my crew and between us we shall decide who will be utilised for baby-sitting duties in the cruise. If, after our discussion, I decide that an inexperienced ( or any other valid reason in our opinion) member of the CC is not to be used for such purpose then that will my prerogative at the end of the day.
Clearly such reasoning is not possible in quite the same way within other organisations where pilots fly with strangers every day.
As 'Framer' suggests, this is a gut reaction solution to a problem that always existed but which the GermanWings incident has brought into sharp focus. If a pilot wants to bring an aircraft down he or she will do so regardless of whom is sitting on the jumpseat. The recent disaster was unusual in the way the co-pilot 'flew' the aircraft and its occupants into the mountains in a controlled manner. Previous similar occurences have I believe been more violent in their inception albeit with the same tragic outcome.