The biggest challenge is convincing people to go back to the native car software. Let's be honest, automakers have done a horrible job at software and it's why Apple and Google saw an opening and took it. Now automakers are starting to give a damn, it's hard to get people to give up what they've been comfortable with for many years. I think GM is smart to just abandon it completely, it forces the owner to use their software. The downside is, if GM's software turns out to be crap then people will leave the brand and go to one that still offers CarPlay / AA.
Lucid has been in a similar boat. If they hadn't fumbled the software for both Air and Gravity would people have been screaming so much for CarPlay \ AA? Probably not. The challenge they also face is trying to convince people they're building a better ecosystem. My stance on CarPlay \ AA is that they have no place in a modern OTA updatable EV BUT the automaker needs to prove that they can actually make good software which has been the uphill battle, even for Lucid.
Also, CarPlay is dying. You can see automakers are dropping it and no one has really gone all in on CarPlay Ultra except a small handful. Automakers simply don't want to give the keys to the kingdom to Apple or Google and rightfully so. Knowing Apple was working on a car, why on earth would you give them all that owner data from your own car for them to take it all and potentially make a superior product? It's suicide.