A recent commit indicates that the Google Pixelbook could receive support for booting and installing Windows from USB, a functionality previously unavailable due to poor firmware support on Kaby Lake and Skylake devices.

screenshot of the commit,
It's pretty clear what functionality this code merge brings.

This update is related to previous reports of Alt OS functionality,  the addition of an Alt OS [Alternative OS] picker screen that we previously suspected could be related to booting Windows or Fuchsia, but it looks like the evidence is in favour of the former being true.

Unfortunately, these updates were merged to a unique firmware branch of the Pixelbook called "eve-campfire," which is different from the normal branch "eve." The campfire branch isn't public (yet) and is being developed and tested internally by Google, so it's difficult to say whether we'll see Alt OS functionality in the wild.

The Google Pixelbook was released in October 2017 along with the Google Pixel 2/2 XL Android smartphones. It's a high-end laptop running an operating system that, for now, doesn't offer the kinds of tools to take advantage of its hardware. That may change soon with the introduction of Crostini to Chrome OS, which allows for running Linux apps on Chromebooks. Bringing Linux apps to Chrome OS is a great way to bring more professionals into the ecosystem, but there will still be plenty of holdouts who are reliant on Microsoft Windows.

If this functionality does arrive on the public build of the Pixelbook, though, it's one matter to boot Microsoft Windows and another to get drivers coded to suit the hardware. Pixelbook owners, don't get your hopes up just yet.

Sources: Chromium code-review, Mr Chromebox [reddit] [website] for his firmware knowledge