*goes to bookshelf and carefully draws Midnight 2nd edition campaign setting book out* What a lovely idea! Can't say I've tried converting it yet. Each tradition has several special abilities to choose from that have somewhat unique mechanics. The same goes for a lot of the classes and PrCs added in Midnight since they are tailored to suit the low-magic of the setting.
I don't think there'd be much to convert. The Defender and Wildlander might need some beefing up, while the Channeler I might either provide with more spell points or just have all magic in Midnight use the Words of Power magic variant coming out in Ultimate Magic which I feel would be a classical compliment to the setting.
Honestly, I would lose the Wildlander and introduce a spell-less version of the Ranger instead and maybe provide a Wildlander archetype as an option. Even the Defender could be made into an archetype of the Monk class to help remove some of the magical aspects and replace them with the more mundane pugilist-style version more akin to the defender.
So either go minimalist and take the setting material as is (it'd be easier to power down the PF Barb, Ftr, and Rog by removing rage powers, armor/wpn training, and rogue talents respectively) or you might find yourself committing to a lot more work converting all the classes and PrC. Even Heroic Paths may need to be balanced depending on the spell abilities offered.
All in all, I'd be intrigued to see what a PF'd Channeler might look like, but I fear a serious revision up to PF standards may require a bit of an overhaul. Still sounds like fun to me though, I might have to give it a go!