That's great! Thanks for putting this out there. Goes really well along side this GUI front-end for the build-script/build-toolchain/update-checkout scripts, I don't know if you saw it but check it out: SwiftBuild - GUI frontend for swift/utils/build-script & build-presets.ini
Latest version has a lot of improvements and fixes. Adding more all the time. For example it will play music in the background and whenever your local build stops it will stop the music so that you know your build has stopped due to success or failure.
I was hoping to put it on TestFlight but it has to access a lot of other directories so I'm not sure AppSandboxing would work.