[@Tangletail] My thought, and [@dragonmancer] will ultimately decide this, is that the mindstones are demonic artifacts. Del Sombra is the goddess of mortal and immortal secrets, but not demonic ones. Demons are fallen angels, according to our GM's post on the subject, and they've undoubtedly changed a great deal. Honestly, I don't think anyone, deity or otherwise, knows much about them except how they're created. Just my two cents.

Also, only a demon can properly activate and use a mindstone. All a god or goddess would be able to do is figure out what it does and who it allows you to talk to.