I suspect the distribution of possibilities considered across our level of ignorance is very, very wide. Even if $1B/day is the peak (which I wouldn't consider

I suspect the distribution of possibilities considered across our level of ignorance is very, very wide. Even if $1B/day is the peak (which I wouldn't consider this anything more than very weak evidence for; no offense to the study authors, this is a freaking hard problem and I respect their attempt to answer the question), I'd expect it to be a very shallow peak in a very wide distribution. There's a lot of unknown unknowns in this space, and a lot of ways that things could cascade surprisingly out of control (e.g., "oops, it turns out that in this particular surprising GPS failure mode that this common model of airplane wants to land half-a-mile west of the actual runway, and while that isn't a problem on its own the modern avionics software is really insistent about that and literally won't let the pilots override, and now the entire air transport industry is on the verge of collapse because nobody wants to fly anymore").