It sounds to me like Chris Lattner just didn't have the expertise necessary. Apparently the new guy is a leading expert in vision and deep learning, and he's coming from OpenAi so he's well know to EM who decided this is the guy they need. This isn't a case of Lattner leaving and needing to find a replacement, it's a replacement by choice. I think this is actually good news and progress is about to get a lot faster.
I mean, Chris is a very talented person with a lot of accomplishments to the tech industry…. But still, you have a team of computer vision / AI guys, and you hire a talented compiler writer who was an upper management figure at another company working on something entirely unrelated both technically and logistically (in terms of release cycles)…. Frictionless would not be the term that I use to describe such a scenario.
I agree, it sounds like they hired a better fit for the role and that was part of a plan to replace Lattner. I really hope Chris finds a better fit, and as does Tesla. There's no reason why this can't be win-win, and certainly keeping someone in a position where the company isn't happy and he isn't happy is not good for anyone.