What HW made clear is that the shape and form of a primal (and Eikon) actually depends on it's followers who summoned it. it's how they imagine their god. even koji once said that if we would encounter bismarck somewhere else he might look different cause they way ppl look at it. that basically leaves open the possibility that we gonna "re-fight" the old primals just with new looks someday.
what we also learned is that as long as you have enough believers (and energy) that almost anything could end up as a primal (go on dalamud fanatics, maybe one day you'll succeed...)
So now the part i don't understand. how is the consciousness of a primal determined? is it some spirit that's brooding all time until it get's summoned into a body? or is it the collective idea of the believers? and in either case how does it contact those before being summoned. we have seen tempered ppl before an actual summon, but who did that to them? some kind of self inflicted hypnosis?
i might have missed the answer to that question down the line somewhere... but if we know it already maybe someone could help out here