Absolutely fantastic move. John Kelly is the complete opposite of everything that is wrong with Washington. He has no ego, is a direct, no b.s. kind of guy, and will not hesitate to fire anyone who deserves it. He has no real political allies, enemies, or outside loyalties. Probably also one of the people most likely to be able to tell Trump uncomfortable truths. The childish games and infighting will stop.
I know him fairly well, and really could not be more impressed with the pick. And he'd be much better in that role than would be someone like Mattis.