"It's my understanding that this is more ancient."
I'm told that it is. Syriac and Malankara Orthodox churches don't have iconostases either in my experience, just the bema and an adorned altar as in the Armenian Orthodox Church. Ethiopian and Eritrean Orthodox churches seem to vary. In North America the ones I've visited or seen all seem to have some variant of an iconostasis, but in Africa many are not built to be able to have one (the octagonal churches) and there I've really only seen the Roman Catholic-style cathedral in Addis Abeba with one, which wasn't actually in front of the altar (it was sheltering the last emperor and empress' tombs :-) ).
Right. The templon, which is the grandaddy of the iconostasis, actually comes into use around the time of Calcedon.