Sadly I watched this accident on radar . . . . both Mode S equipped squawking A and C. Any form of ACAS would have helped. Condolences to all those touched by this tragic but avoidable event.
Having spent half a decade watching the maggots within 15nm of WCO on a good flying day I can tell you that's the last place I would be on a good weather day !!
BUT. . . what staggers me is the amount of mode S equipped aircraft that operated without Mode C (We can tell) either off due lack of equipment knowledge, deliberately switched off (there was was a 14 page thread on flyer about that) or unserviceable.
On one side there are those who demand the right to fly no radio no electronics etc and the other, those whom fly commercially whom want as many layers of ALARP safety as possible. I actually don't think it's the CAA or any ANSP responsibility; it's yours! Get your BGA, BHA, GA alliance et all together to see if they can establish a minimum operating standard to aid airborne conspicuity.
This is the 2nd time this year I've sent radar recordings to the AAIB - 2 times too many.
Stay safe all - Fred