If anything indicated GNU/Linux is mainstream, Samsung releasing a product based on GNU/Linux for desktop and notebook is. The ChromeOS devices are great for people needing mobility or less clutter on desks who mainly use web/cloud apps. As such, a large fraction of consumers or business-users could fit. The price is not cheap but at least the products are small.
A lot of people use PCs differently than they did just a decade ago. Think FaceBook… I know people who spend hours on a single site all day long and only use local resources to upload images. A Chromebook would work for them. A lot of businesses have staff who deal with a single web application all day long. A Chromebook would work for them. I expect Samsung is convinced there is a market and will do the right promotion to stimulate it. That will get GNU/Linux on more retail shelves which is a good thing.