That said, I think most people want darwin failures to be able to block, so it's mostly about getting on top of them to the point where it's practical to keep them triaged. Domen is working on getting a part-time position funded to work on issues here (https://opencollective.com/nix-macos), though individual package breaks are probably down the list.
I feel things have stabilized significantly in recent days, though. I haven’t had a single Darwin breakage on the unstable channel since the release of 20.09. Perhaps the Zero Hydra Failures effort[1] helped.
Recently I had nomad breakage on -unstable caused by nvml support, which pulls in nvidia_x11, which pulls in linux_5_4, which of course not installable on darwin[1]. The maintainer fixed it very quickly (thank you!) but I still need to wait few more days for it to be included in -unstable.