For soft babywearing carriers, the outlook is also grim. The kinematics of the baby, adult, carrier and airplane seat lead to crush injuries that are worse than the poorly restrained arm hold version.
Could there be a solution here that straps around a seat to give babies a safe seat?
Yes, but it wouldn't necessarily be easy to use or consumer friendly. The ideal solution would have the baby with their back facing front, and the attached carrier facing inwards towards the seat. It would have to be carefully specced and tested so no unverified, third-party seats... Logically extrapolated, in this scenario, the airline becomes responsible for the baby's wellbeing. And I don't think that's a good place for the airlines to be?