There’s plenty of evidence that Google will allow some Chromebooks to dual-boot into Microsoft Windows 10; that effort is called Campfire. Although users will have a boot screen to choose their operating system, it appears there may be a keyboard combination upon startup that fires Windows up without the boot screen option based on this code commit.
As shown by the commit from September 4, holding the Chromebook’s power button as well as both the Refresh and A keys will boot directly into an “AltOS”, which
is supports Windows 10. This is currently only applicable to a special, or forked, build for Eve, which is the current Pixelbook.
I’d anticipate it to also apply to the Pixelbook 2, which looks to be a similar device but with smaller bezels and powered by newer 8th-generation Intel Core processors. I’m still thinking that the Pixelbook 2 is actually the “Eve-Campfire” device, not Atlas or Nocturne, both of which are detachable Chromebooks — meaning there will be more than one #MadeByGoogle Chromebook soon. The odds are leaning towards Nocturne making its debut next month, but we’ll see on October 9.
Updated wording on 9/12/2018 to reflect that AltOS supports Windows 10, but may not be limited it that OS.