Here's the thing: if upgrading the hardware is as straightforward as you say it is, than GM is in a far better position to provide true self-driving in its cars.
After all, it's already got the hardware and hardpoints for installing hardware. Swapping out existing LIDAR arrays for newer arrays, or current processors for optimized self-driving processors, would be a piece of cake. Especially with GM's extremely large supply chain, capable of producing more cars in an hour than Tesla can produce in a year, and the corresponding parts for all of those cars.
After all, it's already got the hardware and hardpoints for installing hardware. Swapping out existing LIDAR arrays for newer arrays, or current processors for optimized self-driving processors, would be a piece of cake. Especially with GM's extremely large supply chain, capable of producing more cars in an hour than Tesla can produce in a year, and the corresponding parts for all of those cars.