My 2010 x86 MBP still receives MacOS updates and runs every piece of software just fine.
With the browser being the most important software for the target audience of a chromebook, I think the life could be expanded a lot as long as you can update the browser. Sure, you won't receive OS security updates, but browsers do a pretty good job at sandboxing anyway. A 15 year old laptop with a modern browser should be plenty secure as long as you do everything in the browser.
Obviously, you don't want to do any professional work on a 10 year old laptop, but for the chromebook audience why not?
Does it? My rMBP from 2012 is no longer officially supported since Big Sur (due to a WiFi adapter incompatibility of all things). Not that I have any use for it but it's just a decorative element at this point.
With the browser being the most important software for the target audience of a chromebook, I think the life could be expanded a lot as long as you can update the browser. Sure, you won't receive OS security updates, but browsers do a pretty good job at sandboxing anyway. A 15 year old laptop with a modern browser should be plenty secure as long as you do everything in the browser.
Obviously, you don't want to do any professional work on a 10 year old laptop, but for the chromebook audience why not?