Nor on SYD-JNB.

If you ever want to book this, you would need to construct a South America to JFK to LAX to Asia transit that was the second visit to North America very carefully to avoid falling foul of the "second visit to North America must be less than 24 hours" rule.

I would probably propose starting in JNB for something like:

JNB-LHR-MCT-LHR-HEL-LHR-LAX-JFK-DFW-LAX-NRT-SIN-HKG-JNB

HEL-LHR-LAX will have to be a transit without stopover. Maybe squeeze in DOH between HKG and JNB.