Cpt PB - we are not talking about TCAS 2 and RAs - a simple TAS with audio would have at least got the crews looking in the right direction (especially up/down).
There is no doubt in my mind that if both aircraft in this sad event had been similarly equipped, they would have both known about and avoided each other.
A little yellow blob on a screen with a relative height readout and an audio warning could easily have saved four lives.
Having been through the military fighter pilot training thing early in life, the whole 'lookout' is good training but ultimately hampered by human limitations.