I'm curious: how large is it really? As I understand it, Kakehashi is targeting command line programs, especially Xcode-tools. How much non-POSIX/Mach/BSD interface do Mac command line programs use? How much of that is not already open source. How much of that changes yearly? The only thing that comes to mind is process security for codesign and notarization but I'm just guessing.
The Xcode Tools are written by Apple to run on Macs; they have no reason to avoid internal APIs, and when dealing with App Store-related concerns, they probably do use them heavily.