The rear interior light should also be there as a safety feature to other drivers in my mind.
If somebody was sitting in the back seat and went to open one of the rear doors, then as other drivers approaching from behind, they would see the inside of the cabin light up and know somebody was opening one of the rear doors !.
Apart from the fact it is difficult to load small children into car seats, without the aid of any internal light in the rear of course.
Okay, in the summer of course, but a real pain in the winter months.
Adding the interior lights units themselves, would have been easy enough fix on the ZS EV face lift.
But remember the original model did NOT have any rear interior light also, therefore it would have been necessary to upgrade / replace the wiring loom to accommodate the face lift model.
Also, both rear doors would have needed interior light switches adding to the rear doors also.
They where unlikely to upgrade / replace the loom etc just to provide one extra rear interior light.
It will be included on the next model I suspect.