It's quite clear that the initial commit won't be stable version quality. Targeting this to S3_1 & master only. The intention still is to backport the feature to S3_0 once it has matured a bit.
The patch I'm working on at the moment will add two scripts: 'macOS/homebrew/hbinstall.sh' and 'macOS/homebrew/macapp.sh'.
Usually one does not need to directly run hbinstall.sh, but ability to do so can be handy in the testing phase. It takes one parameter; the location to install to, e.g. "./hbinstall.sh /Applications/freeciv-3.2.app".
macapp.sh has a rudimentary support both for "full builds" and more iterative approach. This is currently determined solely from the prior existence of the target directory; if the directory does not exist, build includes the ./hbinstall.sh step, otherwise not. The target directory is "/Applications/freeciv-<version>.app" by default, but can be given as a command-line parameter.
Split hbinstall.sh part -> #44400
So it can be made available (for testing) sooner. Like in a couple of minutes from now.
With ddeanbrown's changed plans about the macOS packaging, this is now on hold. Likely to get dropped completely.
Working with Dean to create a script for building freeciv .app for MacOS using homebrew. So far discussed on freeciv-dev mailing list.