The primary purpose of Chrome OS is to run applications that are off-topic on Super User (web apps, plus it can run Android apps, both off-topic).
The devices it runs on (Chromebooks), are designed to be used primarily while connected to the Internet, with most applications and data residing online. Their hardware configuration is typically similar to an (off-topic) Android tablet with a keyboard.
Chrome OS is capable of running some lightweight installed apps (to the extent they fit in what is typically minimal storage capacity), and there are some Chromebooks that could be considered notebooks. However, the design purpose is running off-topic apps, and the typical hardware configuration is similar to off-topic hardware.
The tag wiki summary doesn't mention anything about Chrome OS, itself, being off-topic. For that matter, netbooks do not appear to be off-topic. Virtually everything Android is off-topic (OS, applications, hardware), and it is not due to the existence of the Android SE site. So I'm trying to clarify the boundaries of Chrome OS being on-topic.
Web apps and Android apps are off-topic. What about the non-Android installed apps? What about the incorporated browser (is it a completely standard Chrome implementation)?
If notebooks, sub-notebooks, and netbooks are on-topic and Android tablets are not, where do at least low-end Chromebooks fall in terms of scope?
Are questions about Chrome OS, itself (user interface, utilities, interfacing with other devices, system maintenance, etc.), on topic?