thank you for your autonomous vehicle package, too bad it won't work anymore once someone sells a Tesla second hand. You can beat on any bush you want but instead of BMW you should've taken the Tesla example even though it might go against the american pride way of life.
You can already unlock features with Porsche Cars OTA.
I don't mind being able to unlock I don't know adaptive dampers or something as long as it stays part of the vehicle afterwards however Tesla is at the forefront showing how to f*ck things up for consumers.
I wouldn't say you'll find unlock codes all over the place, engine and car mappings are rather well secured and such rental features have to be embedded in the ECU which means unless you have the time for a BFA (brute force attack) via preferrably GPU against the encryption certificate I think the rental features are rather safe.
You can ofcourse take a different ECU, have your car custom programmed but with all respect let me tell you: for your average Diesel or BMW or whatever you won't go down that route because this is a substantial Investment which might start off with a custom wiring loom.