This example is exactly the kind of situation where TCAS could save a life, provided the other aircraft had a transponder.
The pilot broke cloud to find a windshield full of aircraft. There was no time for see and avoid, and, although the RFDS aircraft was lower than normal, both aircraft had every right to be where they were.
My solution:
Transponder mandatory in all controlled airspace and establish an MBZ around all instrument approaches in uncontrolled airspace, plotted graphically on charts with clear vertical limits, and make this transponder mandatory also.
Airmanship would dictate IFR aircraft should not descend through cloud when below 3000' amsl or 1000' agl and not in these protected areas.