I'm not familiar with SeL4 other than in the abstract sense that I know it's a verified kernel.

I interpreted your statement "Then also allow the kernel to run linux as a process, and run whatever you like there, however you want." as the Linux process being analogous to a VM. Invoking an emulator wasn't really the right analogy. Sorry about that.

For me it comes down to this:

As long as the root-of-trust in the device is controlled by the device owner the copyright cartels, control-freak developers, companies who profit end users viewing ads, and interests who would create "security" by removing user freedom (to get out of fraud liability) won't be satisfied.

Likewise, if that root-of-trust in the device isn't controlled by the device owner then they're not really the device owner.

It's what we have now.

I can run an emulator in the browser my phone and run whatever software I want. The software inside that emulator doesn't get access to cool physical hardware features. It runs at a performance loss. It doesn't have direct network access. Second class software.

> . For example, a kernel like SeL4, which could directly run sandboxed applications, like banking apps. Apps run in this way could prove they are running in a sandbox. ... Then also allow the kernel to run linux as a process, and run whatever you like there, however you want.

This won't work. It's turtles all the way down and it will just end up back where we are now.

More software will demand installation in the sandboxed enclave. Outside the enclave the owner of the device would be able to exert control over the software. The software makers don't want the device owners exerting control of the software (for 'security', or anti-copyright infringement, or preventing advertising avoidance). The end user is the adversary as much as the scammer, if not more.

The problem at the root of this is the "right" some (entitled) developers / companies believe they have to control how end users run "their" software on devices that belongs to the end users. If a developer wants that kind of control of the "experience" the software should run on a computer they own, simply using the end user's device as "dumb terminal".

Those economics aren't as good, though. They'd have to pay for all their compute / storage / bandwidth, versus just using the end user's. So much cheaper to treat other people's devices like they're your own.

It's the same "privatize gains, socialize losses" story that's at the root of so many problems.