According to the Ford parts catalog, the Service Part Number for a replacement high voltage battery for a 2017 is CM5Z-10B759-K. When looking up a 2016, that is also what is coming up. I'd say it appears that the new 33.5 kWh is superseding the old pack. It's likely more cost effective to have only 1 part number in such a low volume part.
But I wouldn't run out and buy one just yet, even if you do have $8K+ burning a hole in your pocket :lol: . There will need to be some software updates performed during a battery replacement to "teach" the car that it now has additional capacity and range. I'd wait for the dealers to be notified of this procedure before making any rash decisions.
Just thought I'd share this discovery though.