I just spent quite some time setting up G4 like G3, installing plugins, scripts etc. It would be really, really cool if there was an export/import for this also. It could be just a JSON with stuff installed from Plugin Manager, or something?
In the app settings, you can import most settings from Glyphs 3.
For plug-ins and scripts, there was a lot of unknown compatibility when Glyphs 3 launched, so there was no easy one-click import. Now, the compatibility of extensions is much better, so it could make sense to provide a system that downloads the same set of extensions that are already installed for Glyphs 3. Maybe, that could also have other issues.