Tesla appears to be much closer to general software practices than regular auto industry, creating more software in-house, running multiple permutations of software configurations, etc and purposeful separation between real-time safety-critical systems and IVI.
The complexity of their visible software is immense, the size of the software team appears smaller than required and the time for quality software process is empirically not fully comprehended already. I could only speculate at size and quality of validation of non-safety critical software. The learnings appear to be happening, and the team appears to be expanding, in China has been mentioned. At some point any active software stops, both to minimize additional permutations and because of organic code rot.
I’ve seen changes that were happening to help optimize mcu1 efforts, and supposedly this still happens in a large part because EM paying it back with long term support to the loyal initial supporters, though some because of unintended consequences of improved performance considerations between 1 and 2.
Mcu1 has a fundamental design flaw with its soldered-down flash memory, due to its overuse because of heavy initial telemetry and caching behaviors. Even with this, I would not expect upgrade path between 1 and 2.
The only way to confirm any of this is to get a job with Tesla on software team. Of course, if you did then your NDA would frustrate and prohibit you from saying more..