This post is to suggest adding: Blackguard, Liberator, Divine Champion to the Rainbow Ioun stone use list.
Presently I don't think any of these classes have an Ioun stone attached, and they're all div classes like Paladin, so the most balanced thing in my head is to simply give it the same ioun stone. This only affects 2hers of this class so I can't imagine it'll shake anything up balance wise.