I am a proponent of giving users an option to root their devices through a one-way process that would surrender warranty coverage and print a big safety warning at every boot.

The problem with allowing easy shell access is that any arbitrary command execution would be used by exploits, too. There are also a lot of social engineering schemes that bait users into running commands on devices. We don’t think about these risks as engineers, but you wouldn’t believe how many people will follow instructions to open something like the Chrome developer console and paste code blocks into it because some website told them to.

So a secure device is also a locked down device. Getting a shell is a vulnerability because it’s the avenue that exploits would use.

That’s why I’d be in favor of a one-way developer mode, which provided shell access but printed a big unavoidable warning screen in the boot loader.

Unfortunately, it’s not that simple. Asking people to give up their warrant isn’t legal, generally, so outside of very specific circumstances you have to cover warranty claims on the device, too. I have worked at companies that tried to offer some developer access like this, and the number of people abusing customer service because they got in over their heads with modifications and wanted a fresh unit or want CS to support their mods would make you face palm. So the compromises end up being things like only allowing ephemeral mods that get wiped at each reboot and other default-safe behaviors, but that doesn’t make people happy either.