Problems going from UFOs to .glyphs using v3 file format

Using v6.0.0 I've been looking at Glyphs v3 file format support.

I see that ufo2glyphs does not currently have an option to output in v3 file format. I created an edited version to test with by adding `font.format_version = 3` prior to the `font.save` section and successfully created a v3 format .glyphs file from a design space file. Is that the correct approach to use to create v3 format files?

Round-tripping using that and then glyphs2ufo produced many differences. Some examples are:
- postscriptBlueValues, postscriptStemSnapH and postscriptStemSnapV removed from fontinfo.plist
- styleName in fontinfo.plist changed to Regular for all styles
- com.schriftgestaltung.weight in lib.plist changed to Regular for all styles
- public.verticalOrigin added to the lib of all .glif files

Note with the postscript keys, this data does end up in a .glyphs file if it is produced by saving from the Glyphs App - for example blue values end up in Alignment Zones.