Exactly. Tesla is forward thinking with this stuff. When AP1 came out, it was understood that additional hardware and redundancy would be needed for autonomy.Regarding the ability to upgrade sensors / GPU for later more advanced versions of AP suite:
My Model S was built just 2 weeks before the AP1 hardware was introduced. After the AP1 announcement I have asked Tesla if there was any possibility to retrofit the new hardware to my car. The answer was, that the cost would be prohibitive, because my car is missing the wiring harness in the body panels, so they would have had to take apart and rebuild the entire car.
On the other hand, if a car already has the harness for the right number of sensors/cameras/GPU and it is only a matter of replacing them with newer versions, the cost would be much more reasonable: new parts + labor cost to swap them.
Now, with AP2 out, Tesla has said everything is in that is needed for autonomy. In other words, everything is wired up and ready to go. When better sensors come out to improve the autonomous driving experience, they will be swappable. He's already said the nVidia chip is easily swappable. It's like the 3G to 4G switch. Thing is future proofed now.
Also, keep in mind that Tesla has the NHTSA's ear when it comes to certifying autonomy. Remember how 8.0 was developed with input from them? Does anyone think this system wasn't developed with lots of input from the decisionmakers and with inside knowledge of the details that would make the system achieve certification? I'm placing my bets on Elon here.