Hi,
The act of engaging in freediving exposes you to Black Swan (BS) events, but so does being on the ground or just being alive, obviously to a lesser extent. Diving risks can occur because of: strictly limited and dwindling O2 reserves + distance removed from surface + a need to engage in activity to get to surface + limited field of view + physiologic changes + wild animals + equipment + just being being in water + others. Therefore, if you dive you must recognize that there is a possibility of not coming back because of these restrictions. Though this is the undeniable reality, these are not BS events in themselves, especially since you knew about them. To think so is to confuse BSs with foolishness, i.e., the BS issue is a relative term and depends on your reference point, your knowledge base. For example, the tennis ball with lanyard thing: some knew it was a source of problems, whereas other didn't. Therefore, this is a BS for some but not for others.
".... the black swan event we can not plan for or foresee is what the quick-release system in the lanyard is for. We can build the system to be as robust as possible, but we do not know what issues we may encounter during a dive and must be prepared to abandon the lanyard and FIM or even swim up."
The very act of introducing a new `gadget´ in the hope of bolstering safety has the potential to harbor BSs. The very existence of the lanyard is a source of BSs, i.e., until we find out all its potential problems, which we may not. There now apparently seems to be plenty of reports that the lanyard may actually be increasing the risk of bad s**t happening to you or at least not bettering your situation (on average). If it does not actually bolster safety then you should get rid of it or find another solution. Importantly, one has to be deeply introspective about the difference between real and apparent safety, they are very different and it's very easy to dress the latter as the former, with the effect of falling into a false sense of safety. The bottom-line, you have to really challenge yourself and question what you're doing all the time and be open to other possibilities. Ideas come from everywhere!
I think that one potent way to resolve this problem is to have divers tethered to the surface by means of a back-mounted line and harness, and have them wound up to the surface with the use of a counter-weight (careful here) or reel. This leaves the problem of the reference line. With some thought this need not be an insurmountable challenge either. Years ago, I mentioned using two lines instead of one, i.e., you dive along a track instead of a line. This would be really easy to set-up and would not necessarily result in twisting if correctly prepared. Anyway, there's plenty of really real-world clever people out there these days that could come up with even better solutions.
This is one reason why I personally will not dive to depth that I can not manually swim or pull myself back from - AKA, no NLT dives for me!!
This is a seemingly sound and robust approach, and the best you can hope for given the fact that your are actually freediving, i.e., an inherent risk. To engage in NLT you have to have a good reason. I am opening myself up to BSs, it is risky, I have a good reason, it's not about some empty chase for records, but many think so, that's ok.