TK will not send the A330-200 or A340-300 to JFK. So even if you get the A330-300 you have the new seat. The only TK Intercont destination I know of that gets constant last minute swaps is Bangkok.
You will get lie flat seats for sure between NYC and IST. As I said, a big advantage for me is to be able and get work done on the daytime IST > JFK thanks to WiFi.