Of course, we already know that even by -looking- at Sylveon, there's not really much we can get, it's bodily features don't really reveal anything, and each and every eeveelution's colors usually match its typing. What's unusual here is that we have an eeveelution in which we can't necessarily find exactly what typing it is, because it's colors don't necessary fit a specific type. The closest thing it could possibly come to is either Normal or Flying, because Normal Pokemon don't have any distinct features about them, and Flying Pokemon more or less based on the type/weaknesses image that was posted either here or in the X/Y Discussion some time ago. XD
//wall of text
So far I'm leaning most towards Normal out of everything else. I mean, now looking at it, I want you guys to take a look at Serebii's B/W Pokedex, and go on "search by type" and click normal, and you'd find the results pretty surprising.
Now answer this question after you've looked at that list: How many normal types are Pink and White(or even just pink), and look similar in coloring to Sylveon here?
It has to be at least part Normal, if anything else.
With Eevee already being normal type, I don't see why a normal evolution would look so different