We already know that the Gematsu leak doesn't have all the information; we knew that when Rosalina was a newcomer, and we know that even more now with Robin as a newcomer and Chrom not being one.
However, we also can be fairly certain that the leak isn't just "lucky guesses." The leak has too many specific character choices that were not obvious picks, such as Villager, Wii Fit Trainer, and for me, even Palutena, Pac-Man, Miis, and a newcomer from Pokemon X/Y were not obvious picks.
My feeling? I am glad that the leak isn't 100% true. It allows me to be free in my speculation without someone yelling "GEMATSU" at me. It also allowed me to be pleasantly surprised at Robin's inclusion over Chrom. However, that doesn't mean I can immediately dismiss Gematsu as fake. It would be entirely unsurprising to see Shulk and Marshal, nor would it be disappointing. But they may not be the only newcomers left.