No plans. Instantiate (Mecanim) is a workaround system. It only creates dummy animations so the Animator system knows the events and the duration of the animations. The actual animation data is still inside the json since the skeleton posing still uses Spine's system and not Unity's (because Spine's system has more features than Unity has).
If you need to make or edit Spine animations, you need to use Spine editor.
If it's just previewing in the editor though, if that can be done with regular mecanim imports, that could possibly be done for Spine too in the future.