A quick word of reply about a couple of things:
First: lookout and see and avoid. I fly aircraft, both big and small, in and out of CAS. Lookout is my last line of defence. I don't trust it, but it works most of the time. I simply know that because I'm human, it can't be relied upon. Interestingly, I fly with some people who are very recently experienced in air combat, and I give myself a huge pat on the back if I spot something before they do (this happens quite rarely). This tells me that, generally speaking, you can be better at lookout if you've been trained properly and your life has depended on it in a serious way.
Second: Mode S and Mode C.
Mode S is here; it works; and it's not terribly expensive compared to Mode C. Any move towards mandating Mode C would be pointless.
Yes, there are technical problems with the ultra-compact Mode S kit which is under development, but there's nothing like a blossoming market to sort out the geeks.
There are things afoot in the regulatory world which appear likely to put a stop to commercial operations outside CAS, because it's impossible to put together a reliable safety case against mid-air collisions, and mid-air collisions are quite common.
This might have one of three rough outcomes: either the commercial world stops operating outside CAS, or the other operators have to do something to address the threat that they (leisure pilots) pose to the commercial world (who are there for a purpose, not fun), or there's some sort of elastoplast job in the short term with a view to a better resolution in the longer game. No prizes for guessing how that might play out.
Finally, to mm flynn, the safety case has nothing to do with individual accidents; it's 'big picture' stuff, and I'm not even sure whose work covers the circumstances of this collision. Certainly, it's something the major ANSP would not be keen to associate themselves with, in my view.