Hi Julian,
My suggestion would be to setup a git repo/project and manually pull in the latest 0.92 branch. Then pull in Atsuyoshi’s work, get it working locally, then in CI (travis?) In the interim, packages could be hosted as releases on the GitHub project page; hopefully the Inkscape project would be able to eventually pick up this work and make the github repo obsolete. (I’d suggest deleting the github repo at that point. No need for historic projects to add to user confusion ;-) )
I'd personally rather put effort into helping sort out the official packaging situation rather than work on a satellite macOS packaging effort.
Specifically, I'd rather resurrect the old packaging/macos tree that was removed (http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/15381) so that it can be worked on. It's a bit annoying that it was removed rather than just disabling it and letting it to lie fallow in case people want to work on it. I've got some patches for it that I put on hold when it went.
I wasn't subscribed to inkscape-devel at the time, so am not clear on the background/issues/discussion that led up to its removal. If Martin, ~suv or whoever else could give a summary or link to any discussion, I'd really appreciate it.
Cheers, Tim