Interesting that this got bumped just as I was looking into a few Docker-related items.
The link you posted regarding collaboration isn't really relevant, as that is discussing providing docker images that run OpenWRT in a container. I don't think @mcbridematt understood the goal of the thread either, since that's what he is providing and isn't what the OP was looking for.
This thread started discussing using OpenWRT as a docker engine host - which IS supported in git master and has been for quite a while (first merged in July - https://github.com/openwrt/packages/commits/master/utils/docker-ce ). I just discovered this last week, and strangely, there's NO discussion of this fact anywhere I can find. Any Google search for Docker and OpenWRT is looking at the opposite use case (OpenWRT within a docker container), or using a Docker container to facilitate building OpenWRT on hosts that don't play nice.
I can say that docker-ce running on an aarch64 Raspberry Pi 3b+ runs pretty well. The main issue is that you really need an additional storage device beyond the SD card, at least on pi, because sysupgrade will clobber the partition table, so you can't readily put a third partition on the sd card for persistent storage outside of the rootfs. If you've got Docker images there, it's way too much for sysupgrade to try and back up into RAM when the rootfs gets nuked.