I'm happy to share a new extension for Adobe Illustrator that allows you to open/import, edit, and create/export to IconJar format directly in Illustrator : Icon Mason. This product was created with the full support and some help from the folks at IconJar.
Unlike IconJar, Icon Mason is compatible with Windows (with a minor caveat discussed in the documentation).
In addition to IconJar support, Icon Mason allows you to import ZIP archives as well as regular folders.
A 10-day free trial is available.
Check it out at IconMason on aescripts + aeplugins