For the record, I use the aforementioned
Syncthing to sync across 5 machines: 2x macOS, 2x Linux, 1x Windows (I have too many tablets and tools).
.stignore settings are:
The first two lines are the most critical.
I'll translate for non-Syncthing users:
1) yes, include the single package on all syncs for .atom/packages/package-sync
2) now, ignore ALL OTHER .atom/packages/* in this directory.
What this does is for new Atom installs using this sync'd local directory, it installs the single package Package Sync only. After it loads that package, I run
Sync from with Atom and it loads up all the packages.
This gives me a tad bit of fine grain control over massive upgrades and reconfigurations - before it's sync'd everywhere.