One nice thing with Google WiFi being based on CROS, is that it's mostly open source (about the same level as Android, where there are some binary blob board support packages). With that, there is custom firmware you can load know Google Wifis: https://github.com/marcosscriven/galeforce
I think there is a pretty big distinction wrt routers, in that an end-user cannot build it. That link states as much under the, "Why not just build Chromium OS from source" section. Has anything changed ? With android at least, google distributes the blobs. This probably (?) explains why openwrt hasn't been ported to any of the google routers, although the availability of chromiumOS source would make you think that it would be straightforward.