I’m pretty sure that’s just a bug affecting some SR+ models as most of them do not have an option to enable the heat in the rear seats. Whether or not it gets corrected with a future update is anyone’s guess.
Since neither the SR or SR+ were supposed to have rear heated seats this has nothing to do with a planned downgrade. It’s just a bug that slipped through QC affecting certain vehicles. Enjoy it while you have it but don’t expect it to be there forever.