The AC700 does have a developer mode. That doesn't mean there's any Linux distribution which will install on it.
For a while, there were, but they disappeared, and now it's a web of 404s and obsolete documents. Most recommended chrubuntu, but (1) that relies on obsolete ChromeOS components, which introduce security issues (2) someone said that's now dead too.
I'll see if Chromium builds for it. Thanks for the pointer. There's a lot of AC700's out there.
There's a whole pile of AC700 Chromebooks around, with no upgrade path as far as I know, at least if you don't want to be p4wn3d.