[SilverBirch]

>If Rivian’s native UI is so great, then their customers… won’t use CarPlay. It’s that simple.

I kind of disagree with this. Airpods are purely additive, customers can just choose to use different headphones with their iPhone if they want. But they don't want, because Apple lets Airpods interact with the iPhone in a way that other manufacturers can't.

So no, carplay wouldn't be mandatory but it's likely that Apple's leverage will kill their in house offering.

[NetMageSCW]

It’s up to them if they stop working on their in house offering. If it is inferior, people won’t use it. Apple doesn’t have any leverage over what they develop.