Don't let me put words in bast0n's mouth, but there appear to be two seperate but linked events here:
(1) The undue haste with which the HISL mod was released to service.
(2) The collision between the two aircraft at night.
Our current propensity to line up the "holes in the cheese" seems to conveniently overlook some fundamental principles of airmanship that have been taught since (night) flying began. If these two aircraft had been oblivious of each other's presence and had the mid-air, then the HISL condition would obviously be a significant factor. Given the mutual awareness of the respective aircraft, the need to formate at night and the near head-on closure angles, then the HISL's condition is contributory but not necessarily causative.
Vertical separation, radar assist, pre-briefed joining patterns and use of nav lights were all tools and techniques that would or could have prevented this tragic accident. To focus on the HISL mod to the exclusion of questioning the execution of basic airmanship skills is not likely to reveal all the lessons that could be (re)learned here.