Can the system "tank turn" around an arbitrary point instead of the center of the vehicle? I can imagine some situations where a tank turn might be useful but a common scenario is parallel parking where I would prefer to pivot around the rear bumper.
No, that's based on sideways slippage. How a tank or a Bobcat construction vehicle turns.
The article title says 80 degrees. My layman understanding is rotating in place means 90 degrees. Correct me if I'm wrong.
Think about a circle that has the center in the center of the car, and all wheels on the perimeter. Then each wheel has to turn along the tangent of the circle. That is the circle each wheel will go along when the vehicle is spinning in place. So it's less than 90 degrees. For example the left front wheel turns right, a bit less than 90 degrees.