From another thread:
I feel like if we take this approach, it may make moving easier either now or later since we wouldn’t need to move an entire fork of nixpkgs, rather just the parts we are working on (although it may grow to nixpkgs size in time). I feel like starting off directly with a fork of nixpkgs will be too much to maintain, especially starting out now. I imagine the core repo importing nixpkgs as a flake input, with other package groups importing the core, and then have a top-level repo (auxpkgs or something else) exporting everything. I think building something from the ground up might be easier than breaking nixpkgs apart to fit our new mold, and could also allow us to more easily move away from GitHub.