extracting product.img (2668 MB) to disk...ziparchive W 03-21 17:28:03 30314 30314] Zip: unable to allocate 2798404236 bytes at offset 0: No space left on device fastboot: error:
I don't think I understand "Crouton wasn't really an option". Crouton is a simple script that installs various versions of Linux desktops that run alongside Chrome in a chroot. Probably any Chromebook made can install Crouton. The only thing required is to be in developer mode, which you are. I choose to run my sessions in a tab but it can be a separate window. Not much you can't install and run in these sessions.
fastboot doesn't report version but adb is 1.32 which is old. I don't know how recent adb was added to Chrome OS but I am sure I have used them in the past. I have lived in Canary for the last 2 years so I have no idea whether it was a Canary thing or widely available within developer mode.
Another option since you are in developer mode is Crouton and install a fullish version of Linux. adb does work within a Crouton session. Even if I was to update the version installed in Chrome OS, I would need to reinstall it every day since Canary is updated daily and sometimes two or three times a day. Even stable can be updated mid-cycle so you could get caught with the outdated one at an inopportune time.