The rumour bouncing through my recollection is that a NPRM framework has not been used previously for FSB or JOEB processes. Caveat: I don't know -- but if it had happened before, would it not be the case that the particular airworthiness certification question or set of issues would be known and would be attached, in the pro pilot community, to the basic background about a given type of transport category aircraft or a given derivative model of a type of transport category aircraft?
If I am recalling properly the EASA position publicly has been stated as having a preference for a third AOA input or, as a possibly satisfactory alternative, input of synthetic airspeed. I agree with the assessment that the opportunity for comments by disparate authorities and experts (some of whom might not be actually expert or authoritative) creates a potential for a long and drawn out, and convoluted, process (if that is a correct reading of safetypee's post).
Can't help but wondering if the Special Conditions which were part of the 787 type certification with regard to its use of lithium-ion batteries had been subjected to NPRM for commenters far and wide, what result might have obtained? (That is, on the assumption noted above that the NPRM process for 737 MAX now is a one-off, first-time deal, in Dep't of Transportation/FAA's ongoing efforts to cope with the monumental shooting-in-the-foot by the manufacturer.)