Thanks to the suggestion and code contributed by @zombyra in issue #6, we now can carry over bones parented to the metarig to the Final Godot Rig. For example earings, ponytail hair bones, tail bones, extra arms, etc. So spin up a the Rig of your choice, add more Rigify sample bones, and parent them to whatever bones you like and convert the rig for Godot/Unity, etc.
WARNING: Not all Rigifiy sample sets work great. Some are very particular about their setup and may need some finessing. Some are simply fussier than others. For example, the super face. Upgrade the face first, then parent the upgraded face bone to the core Metarig and THEN Convert to Godot. It should convert fine, and still be parented to whatever bone you parented it to on the core metarig.
Exciting stuff.
Also, per several complaints of the base Rigify/Mixamo proportioned bodies having too much ape index (long arms and hands), there is now a Godot Rig for a "Natural Human", which has a more typical proportion. Shorter hands, fingers and shins, higher pelvis, with thigh set at it's base (slightly ignoring what Rigify's documentation shows) i find gives better butt/leg deformations. Etc. Many small changes. Hope you find it useful.
