The Pixelbook, labeled as “eve” in the Chromium Git, was tagged with a branch called “campfire” and had references to an “Alt OS,” almost definitely Windows 10. Now, we’re learning that multiple Chromebook models may be able to support Campfire as device branches have now been merged upstream, so the project is now coming out of the trunk.
Campfire seems to be intended for public use as efforts have been made to not require entry into Developer Mode. Official updates to this feature will be sent to a partition called RW_LEGACY — it will need at least 30GB for the Windows ROM itself.
This feature is heavily hinted to be part of the Google’s October hardware announcement.