Just having an option to add folders without adding anything from them (as with zip when you don't add '-r') and to not sort anything in some alphabetical order should be enough to allow users to add a _MACOSX folder with AppleDouble files (which they can create using other utilities) in an order that's compatible with archivers that can recreate resource forks from those. 7zip has to do less things than it does to make this work. zip archive because the order in which AppleDouble files are added seems to be important for this to work properly and since AppleDouble files have filenames that start with '._', sorting them alphabetically just seems to mess up the order in which they should be added for this to work. just to summarize.ħzip doesn't have to add any special support for resource forks / extended attributes for this to work (since AppleDouble files can be created using other utilities), other than to have an option to add a folder without adding the contents of the folder at the same time and to not sort all files in some alphabetical order when writing them to a.
Before I write some more detailed explanations. it's important for aliases that are created in Finder to work, it's used to preserve tags for files and folders, for custom icons (if you go to Get Info and apply a custom icon there).
As you probably know, preserving resource forks / extended attributes can be very important for some files like old Mac fonts.
