Moi/, there should be no need as there is already someone in such a position. The set up at AMS for remote de-icing is that the pad supervisor is in contact with the rigs, de-icing control and the aircraft. He is also mobile (small Mercedes 4x4) and from that position, should be able to determine that all de-icing trucks are clear. On completion of de-icing, you are told the start of your holdover time, the fluid/s used and the last phrase normally uttered is "...and all de-icing vehicles are now clear. Please re-contact Ground for taxi."
What is unclear is what knocked the truck over. Was it the tail or was it jet blast? Either way, the de-icing truck was vulnerable as soon as it had completed it task.
PM