IMO, you're confusing A321 and B738.
A321 has -S domestic version, -H ETOPS version - both two class. There's also a -T transcon three class version.
738 is two class, and many, not all, have seatback IFE. The 737-8 MAX will have onboard Internet server with IFE streamed via WiFi; narrowbodies without seatback IFE will pretty much have this. Those with seatback IFE will still have it.
Your JFK-SAN 738 will either have or not have seatback IFE, and it's not predictable.
See
http://www.flyertalk.com/forum/ameri...ec-2013-a.html, and
http://www.flyertalk.com/forum/ameri...s-ife-etc.html for a list of links to AA aircraft and related threads.