Historically, I’d say that the chances of this being successful are exceptionally low given how large the ABI surface is — and it will wildly change out from underneath you on a near yearly cadence.
Perhaps LLMs change that calculation. I really couldn’t say.
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.
Even React Native tools used by tons of companies struggle to keep up with Xcode build tool changes on mac itself.