First time poster here! 
I've been a fan of Jim Butcher and the Dresden files since I first read Small Favor back in 2010. 
I've been wondering lately if Mac wasn't Fae after all. Could he possibly be of the angelic variety? A grigori? Or maybe the scion of a grigori and a human (or Fae!): nephilim?  I mean if Kincaid's the scion of a demon and a human, shouldn't there be an angelic version? I don't know if this makes a lot of sense. Hahahah. But Mab respects him (and she doesn't respect lightly) and he seems to be older than he really is. Stronger than a normal human, and very knowledgeable of anything supernatural. 
Also, Harry's mentioned several times in the books that Mac's brews are heavenly. Could this be a clue? Am I grasping at straws here? Hahaha.