The ChromeOS use case is a strict subset of the use case of a normal Linux laptop. There is nothing stopping you from treating an Ubuntu installation as if it's as limited as a Chromebook. It's every bit as lightweight and can be every bit as locked down.
I've never seen the security stuff from ChromeOS be ported to live outside of ChromeOS. When I looked at it (trying to build the inside-container agents for acustom container image), the error messages for setting it up incorrectly were.. let's charitably say hard to understand. I doubt anyone outside of ChromeOS developers understands it, really.
It's pretty intricate, e.g. giving Wayland access to virtual machines in a safe way.
The hard problem of security is giving the user the power of a general-purpose machine without exposing them to the risks. "Don't run your favorite software lol" is not a valid approach to security. ChromeOS remains totally unsuitable for even casual usage, let alone anything serious.
Someone will, I'm sure, claim that the use of virtual machines is a solution. It isn't. The layers of virtualization in ChromeOS lead to atrocious performance, reliability, and functionality. I am not willing to tolerate half my programs living in a different universe from the other half, nor am I willing to tolerate uptime measured in hours.
I'm not sure what you mean by uptime measured in hours, it seemed fine to me in the years where I used it.. It also provides all of the common computing including all of the browser debuggers, etc, the state of common computing might not be that impressive but that is Windows, OSX and Linux' fault.
One could argue that anything you can't do on a ChromeOS machine (or an equivalent Firefox one if that project were more complete) without running a VM is proprietary garbage. The other Apps you will run will work on some percentage of machines, the device you use have incomplete drivers, the window environments they developed for were not worth standardizing such that a browser has to provide the standards layer.
