Spoke with an inside source. Wiring harness is there and leads to the LR tire area. Issue is that there is no "brain/ECU" or sensors installed. That individual didn't now whether it would have retrofits for existing cars though.
The ability to create revenue after delivery is certainly one of the interesting differentiators for Tesla.
The parking sensors are obviously something that can't be done as "just" a software upgrade. But if the rumors are correct and the main wiring harness does have the wires needed, then changing out the bumpers seems feasible. Rest assured it will be VERY expensive. They charge EUR500 for the factory option in the EU - that appears to translate to a USD500 factory option here (if you compare other prices). My bet is a retrofit will be at least $3k.