ChromeOS updates are actual feature updates - for the 10 years of support, your device will be tip-of-tree and have all the features (except a few which are flagged-off, usually for business or performance reasons)
Yeah, you're right. I got a little separated from the comment chain here after writing about the Nvidia Shield and what it implies about phone lifecycles by conflating that story with talking to ChromeOS. While the Shield received major kernel version updates as recently as 2 years ago, going back to the actual comment discussion around the abstracted ChromeOS userspace vs firmware/kernel/driver layer ChromeOS does already drive feature updates of the upper segment of the OS for the full lifecycle without requiring the kernel updates seen in the Shield example. Good catch and thanks for the correction.