My guess is that it's a Normal type. It'll be interesting to see how Eevee evolves into Sylveon. Stone? Friendship? Level up via a certain Route? Contest stat (like Feebas to Milotic through max beauty and level up), a good excuse to bring back contests and to connect to the eventual R/S 3DS remakes? Or perhaps via new method? In the video, it showed a variety of attacks, such as that large sphere attack, an attack with cards, and stars (it looks like the move Swift, a Normal type move), so it looks like a Normal type (Plus I would've thought a Flying type Eeveelution would have the common characteristics of flying types, wings).
CraigEmberson wrote:Flying type... Flareon, Umbreon and Leafeon are all directly opposite to those they are most effective against. Jolteon is opposing Sylveon, meaning she could only be a flying type if this pattern is anything to go by.
A great deduction, but Leafeon (Grass) is weak against both Flareon (Fire) and Glaceon (Ice), but strong against Vaporeon (Water). Vaporeon is strong against Flareon, but is weak against Leafeon and Jolteon (Electric). Glaceon is weak against Flareon. Umbreon (Dark) is strong against Espeon (Psychic). So that wheel doesn't show simple opposites.