1/ I know close to nothing about automotive software. But I know software in general, including other niche verticals. It's clear to anyone who ever worked with software that code complexity and bugs/functional errors/security holes are exponentially related.
2/ Bulls praise Tesla's single CPU approach vs the distributed systems of legacy auto. True, it gives the opportunity the develop new features much faster and cheaper.
3/ It also enables Tesla to OTA new features that are impossible for legacy to do with their distributed systems, especially that some come from contractors. Asterisk impossible and rephrase it to take an extremely long time and cost.
4/ But software testing is an art if you have monolithic code. In a distributed architecture that is well-designed, modules interact via properly defined interfaces and API's. That's orders of magnitudes easier to test and is much less prone to errors.
5/ Tesla's approach results in fancy features early, but you'll see UX freezing, systems rebooting, cars shutting down... and SUA. Sounds familiar?
6/ Legacy lag behind in many if not most aspects when it comes to software. In theory, they could align systems, but I just don't see it happening in the near future. Tesla will, for its existence, have a lead over legacy in terms of features. Just as errors that affect safety.
7/ And security. That's gonna be an issue real soon. With enough cars on the road, some would be interested to get info about whereabouts of some owners (current and historical, including typical commutes), camera pics and in-car conversations (if applicable).
8/ Others will like to take control over 2 ton+ vehicles that have a 3.6s 0-60. A single one or many at a time. In NYC+DC only or countrywide, or worldwide. On 9/11 or 4/20, maybe.
9/ Again, this is a risk for legacy too, but with their simpler codebase and distributed architecture, it's easier to avoid (and still not all of them are connected yet). TBF, this architecture isn't their choice, it's inherited, but here we are.
10/ VW is developing a whole new SW system, VWOS. It's yet to be seen if this will be monolithic, similar to Tesla's (rumor is that an early version will run on the ID.3 and that caused them to announce only summer deliveries for cars being produced since last Nov).
11/ To add some pictures to this boring thread. Source: VW. They estimate $1 billion lines of code for L5 autonomy (aka FSD). 
