I know there's been a bit of talk about the gif a little bit back, and the speculation that the move is either Brave Bird, Sky Attack, Focus Punch, etc. but...
What if it's just Hidden Power? It seems to me they picked attacks that all the Eeveelutions can learn to showcase Sylveon. Trump Card, Swift, Hidden Power...all moves that can't be used to ascertain its typing.
As for the other picture that's been posted, of Eevee with the Eeveelutions all in a circle around it, there's something about them being super-effective against eachother, but then they're also tiered like this: First row--Wave one of Eeveelutions, in numerical order of Vaporeon, Jolteon, and Flareon; Second Row--Wave two, numerical order of Espeon and Umbreon; Third Row--Wave three, Glaceon and Leafeon; and Sylveon offset at the bottom.
I think this is more likely the case than the speculation of "this one next to this one is strong against it, so Sylveon must be arranged the same way!"
I'm not saying anything for or against Flying/Light/Whatever, I'm just saying that what we have now doesn't present us with any particular new evidence.