I get warnings when I have config.warnUndeclaredOptions = true; set on attributes: config.replaceStdenv, config.cudaCapabilities, and config.cudaForwardCompat. Maybe we could add these to pkgs/top-level/config.nix? Feel free to close if there's a specific reason they haven't been added that I'm not aware of.

I guess some immediate difficulties arise around what the type of replaceStdenv should be, and similarly what the type of cudaCapabilities should be if it's not set.