Using niche open SoC will make the device slower and/or more expensive. The mass market cares about price and performance.
The evidence for this is that people didn't refuse to buy the first generation of unrepairable devices. Because nobody told them they were unrepairable until they broke, and by then they already owned it. And by then the unrepairable devices were all you could get.
How many people would buy a phone if you could honestly market it as lasting for ten years instead of three and having a lower repair cost when you drop it on the concrete?
> Using niche open SoC will make the device slower and/or more expensive. The mass market cares about price and performance.
The mass market doesn't care about performance on mobile devices. They can't even tell the difference. It's all marketing. Even the phones that are actually faster on paper aren't faster in practice when the "slower" one still does everything instantaneously.
And then on top of it you can add all of your Google-alternative libraries and services, which need not be perfect immediately to get people to use it because they can start off running Android apps and buying it for the open hardware. But as you get more users, the software improves too.