Like most "Simple" solutions, the devil is in the detrail:
https://travel.gc.ca/travelling/chil...-plane#systems
By the by, it is not simply up to the FAA, each country served would have to approve the seats and also change their laws to require them to be used. Then of course the travelling public (you know the ones who like cheap low cost carriers) might not be happy and would lobby their local governments .
Here is a link to what is being researched by Transport Canada.
https://tc.canada.ca/en/mandating-ch...rcial-aircraft