Chrome OS' codebase is publicly available, leading to the discovery of news about changes to the OS that could end up coming in the far future or even not at all, and the latest of these is the possibility of Chromebooks with 4K resolution screens. The mention comes in a commit from contributor Julius Werner, who uploaded a commit that patches the current Chrome OS boot logo for higher resolution and better clarity, which will increase detail. This has the side effect of making the icon look good on 4K screens, which Werner mentions in passing at the end of the commit, seemingly joking about "secret" future 4K Chromebooks. It is worth noting that no other information pointing to support for or the possibility of 4K Chromebooks has been found.
Laptops typically come in screen sizes up to 17 inches, though some can reach mammoth proportions, such as the infamous HP Dragon and Acer's recent Predator 21X gaming laptop. Current Chromebook models only get into the 15-inch range, which would mean that a 4K resolution could mean in excess of 300 pixels per inch on many models. While a small phone screen that's held close to your face or used for virtual reality will see a big benefit from a 4K bump, a laptop screen is typically kept a bit further away, which would make the jump between something like 1080p and 4K a bit harder to perceive in most use cases. Still, it would mean more room to move applications around and get work done, and the ability to display 4K media, at the very least.
One key thing that takes this mention from a gimmick or possible joke into the realm of true benefit is the fact that Chrome OS detachables and tablets are on their way to the market. A Chrome OS device in tablet mode will potentially have its display shared by multiple users, or viewed at closer range than a laptop. This would make it easier to spot tiny details in media and games, and otherwise genuinely benefit from the addition of a 4K display resolution in the Chrome OS device lineup. This change could also apply to future Chromebits and Chromeboxes that can support 4K displays, though the market for those two device types has been fairly quiet for a while now.