> - a workforce with sunk costs in last generation skills

Often a unionized workforce. You didn't want to use more robots on your assembly lines like Elon Musk, did you? Because these guys are still going to be employed. Period.

I don't think these points are of any relevance. Once you have stage IV autonomy, you can partner with any car manufacturer you want, you have all the leverage.

However, knowledge in cars definitely helps building the technology, since there are so many little variables that you otherwise would oversee.

You can try to partner. However all major auto manufactures are looking at self driving cars. Some are doing it in house, some are having and existing trusted partner do it. That minor auto manufactures have partnerships with someone major and have reasonable confidence that their major partner will provide the technology.

Apple and Silicone valley in general is not a trusted partner, in fact they are the opposite: untrusted. Car manufactures have lost millions of dollars on safety lawsuits. The cowboy coding culture silicon valley has a reputation (not always deserved) for doesn't work, they need controlled processes where they can show the courts they made effort to check everything, starting with the design phase.

Car makers expect that they will be sued over a 10 year old car with some parts failing. They need to show the court they did everything possible to anticipate that exact failure case and either ensure it couldn't happen, or if it they handle it. When someone is dead, "we didn't think about that case" doesn't cut it.

In short, I don't think Apple or google will get anywhere in self driving cars. They have early demonstrations, but that doesn't mean anything long term. It doesn't even prove they have an early lead (though I suspect they do) since car companies might or might not say anything about where they are. In fact in this case I expect them to be very careful not to say anything: if they say to much a lawyer might argue the car should have been self driving and thus the car manufacture is fault for an accident. As such they need to set expectations that self driving cars are a future thing that isn't ready yet.