Let's look at the Fairy type, and what is rumored about them. At first, noticeable is that there isn't anything known that Fairy might resist, which is odd, especially considering the two weaknesses the Fairy type has. That being said, there is more about it and I assume more resistances and weaknesses on both sides of the spectrum have to be revealed.
There are also too few types that resist Fairy, I think, and as such, that the leak only told half the story. Thinking about fairies, numerous weaknesses and resistances come to mind. And as such, I am going to feed the rumor and make my guess. Things with a question mark are things which are even more guesswork than the rest, and things marked as confirmed, are, well... confirmed and as such not a guess at all.
Fairy offensive:
Strong against: Dragon (confirmed), Fighting (?), Dark (?)
Weak against: Grass, Fire, Psychic, Steel, Bug (?)
Neutral : Everything else
Fairy defensive:
Immunity: Dragon (?)
Resists: Fighting, Grass, Bug, Dragon (?)
Weak to: Poison, Steel, Normal (?)
Neutral: Everything else
Uncertain: Dark
A few things are obvious; Fairies won't harm the nature they live in, but they aren't harmed by them either (mutual resistances to Grass and Bug). Fairies can't really touch fire and smaller ones are afraid of it, (and as such, Fire resists Fairy), though larger fairies (giants and witches) probably won't be too bothered by it (and thus, Fairy is not weak to fire). Creatures with a powerful mind won't be afraid of fairy magic and can possibly easily deflect it through psychokinesis (Psychic resist).
In folklore, Fairies slay dragons (translating to weaknesses as well as resists and a possible immunity), and it's pretty hard to hit a nimble fairy with a fist, or to actually hurt one if it is a giant (resist to Fighting, possible weakness). Fairies in folklore are often killed by sword, much like witches and other magic creatures, whether humanoid or not (translates to being weak to Steel as well as Steel resisting it). Fairies despise toxins for obvious reasons, even more than anything else (resulting in a weakness to Poison).
That being said, humans often killed people rumored to be witches and the likes in the past, and as such, Fairies are weak to (stupid?) Normals, provided GF is willing to give Normals a type advantage to something, that is.
Then there is the match-up against Dark, which I don't know squat about. Fairies and fairy magic in some tales and ESPECIALLY recent stories is extremely effective against evilness (Harry Potter as well as Eragon comes to mind), while taking nothing from it in return (again, Harry Potter comes to mind). However, Fairies also despise evil and trickery, which could translate to a weakness as well, but though ambivalent, also to a resistance as they are equipped to deal with it better than most, especially in the numerous elf stories out there.