Nice! I saw this too. It seems like additional work is required to implement each OpenWRT release in unsupported hardware. I'm not a firmware developer, hence not familiar with the process. May I know what's required if I were to include support for a new device?
And secondly, does that same work have to be re-done by someone for every release? Or does it mean that once the hardware is supported, then each subsequent release will just require a sysupgrade?
It works like this: new software and devices are added to master/development branch and every year or so the master branch is split to create a stable release.
Since this device is not going to be merged in time for 21.02 (which was split months ago and has been stabilized), you will have to wait next year(s) when next stable release appears, so 22.0x or whatever.
Until that time, OpenWrt will only provide development snapshot images for your device, which are a bit more annoying to work with.