It seems less people are involved or interested in solving the Darwin related issues. I have more issues getting things built and installed on OS X compared to a year ago. This mainly because it seems people aren't really interested in maintaining the OS X part of nixpkgs and some simply lack the resources to do so.

In the end it seems that this will get better if it can attract enough OS X users so that patches start rolling in but right now it's just a few people fighting that battle.