stds-802-16-tg3: RE: support for AAS (C802.16a-02/49)
I don't believe that that analogy is quite correct.
As you correctly state, no matter the IDcell in use by the BS, the SS is capable of complying with it by scanning the DL signal. This is not the case with the proposed text, since if the BS is using this optional mode, the SS isn't going to find any suitable IDcell, unless it is also capable of the optional carrier allocation.
However, if you claim this dual implementation is simple (I didn't have that impression, especially on the DL), then there probably won't be any objection to making this particular permutation mandatory as well. In that case, interoperability can be achieved by the (in your view simple) additional complexity of the capability to detect (SS side) and select (BS and SS side) reception and transmission of either carrier allocation.
I guess that could be a viable third alternative to creating a compromise carrier allocation or not including one of the current ones. Any of these three choices would then result in a single interoperable OFDMA PHY.