Hi Mike,
Over the past few days a small group I'm affiliated with has picked up development from the FydeOS and FlintOS chromium for raspberry-pi.
I personally don't plan on building for anything less than a pi3 as I believe even that will struggle. I know there are ARM64 releases of linux for that and the 3b+
The problem I personally would like to solve is build complexity (5 steps and one type-in takes a potential dev-user from git clone to fully built chromium OS).
Some of the problems I'm running up against at the moment are build nuances, where to find facts (everyone in the chromium for rpi believes x11 is dead, it very much seems to be an option to turn off).
Currently 56 is the only build that boots, so it's not new. But I'm sure with more help from internal Chromium teams and expert users of chromium build we could easily get a system up and running, merged as rpi3 or similar.