A few people seem to have confirmed this isn't actually true - at some point, it was possible to set up at least some of the affected NAS devices using btrfs vi

A few people seem to have confirmed this isn't actually true - at some point, it was possible to set up at least some of the affected NAS devices using btrfs via the standard GUI on the device. It's possible there were some intermediate software releases which disabled that but still allowed existing btrfs volumes to be used.