Just finished reading the Shining, and I can't help but to be curious about the Divination Key. A few questions, tho.
While I realize they are obviously geared towards healing and buffing the other characters, would it be possible to include some forms of exorcism into the class, allowing them to handle themselves in combat against demons to some extent? 
Also, since I am not the GM, I think it would be difficult to accurately apply premonition during the RP. Have you thought of how this would be executed in game?
Also, I'd like to delve into demons having private, telepathic conversations with my character at some point, and an internal struggle of fighting off the voices in his head. Perhaps, even, demons getting into the other player's minds, and my mage noticing and helping them mentally ward off the demons as well.

Just some ideas :)