It appears Project Campfire, which was an initiative that was meant to enable Chromebook users the ability to boot Windows or Linux, is no more.
AboutChromebooks reported the closure based on comments and code removals on Chromium that have make it very clear Google is no longer working on the project. One example explicitly marks the “AltOS” mode as deprecated.
While it might seem to be unsurprising that Google is pulling the plug on Project Campfire, it’s also probably to be expected given that work or even news on the project has been relatively quiet since it was announced in December last year.
There was no direct mention of the project from Google, and it seemed only the company’s own premium Pixelbook (the future of which also seems to be under a cloud) would support the change in the first place.