Maybe the love theme is pretty strong in Sylveon, as posted above. It might be a new type, or it might be an old, but either way, maybe it will be a running theme. It can be pretty love-themed without being of the "love/emotion" type (emotion for more applicability), seeing as its ability can reflect most traits GameFreak care to give it. We all know Primeape is notoriously angry, and thus it has Anger Point and Vital Spirit as its abilities. Slaking is lazy, with Truant (and moves like Slack off and Yawn). Dragonite is said to be able to control the weather, and thus gets almost all the weather moves in the game, and so on. Even without restorting to a new type, GameFreak can make Sylveon pretty love-ey.
A Love-type seems like an interesting idea, but it would be very hard to make type matchups that would make sense with it, bar against Dark-type (and maybe Steel-type - as machines don't feel emotions, but this is very debatable as Magnezone FEELS emotions according to its PokéDex entry). Then again, A Love type would be a good replacement for a Light type, though I can't imagine what types it could hit super-effectively, or not very effectively, or what it would resist or be weak to. Speaking of which, imagine if they changed the Attract mechanics so that it could affect same-sex Pokémon. It would be an act of respect from Game Freak to recognize that homosexuality is natural and that gay couples should have their rights recognized, Although Game Freak would possibly have problems with the Church.
What does the prefix "Sylv" derive from?
Right now, I'm thinking the Slyph theory may be the most likely. According to what I've read about Sylphs:
Sylphs are winged air elements or fairies. They ride the wind, flying high with eagles, Sylphs are almost transparent. They're slender and graceful, with large glistening eyes and huge wings. Sylphs befriend and protect other flying creatures, such as birds, moths and butterflies. Sylphs can move as fast as lightning, but they may also drift along on draughts or puffs of wind.
Almost transparent - Slight stretch, but Sylveon is predominately white-coloured.
They ride the wind - I believe some made the connection between the bows and scarfs with kites, which would make sense as kites can "ride the wind".
They're slender and graceful - The lightest Eeveelution.
Large glistening eyes - Sylveon has massive blue eyes.
Butterflies - Some people thought the bows looked like butterflies, and this is where they could come in.
I think there are more definitions of Sylphs which... I'll check out. Again, maybe knowing the origin of this mon can give us a hint towards its stat spread? Sylphs are described as moving as fast as lightning, and they befriend and protect other flying creatures. Perhaps a fast, defensive Flying type? Something along the lines of 65/60/110/65/95/130, though more HP would be nice. And just an extra: if Sylphs move as fast as lightning, and Jolteon is an Electric type, it's possible that Sylveon will have the same speed as Jolteon.
I'm actually more interested on how it evolves. Maybe this is a stretch but:
Maybe? Although, we can already technically trade Eevee holding a Prism Scale in Gen V. Another thing I'm wondering about is it's ability. What's it's ability going to be? Something new, or related to Flying/Wind in general? Or something basic like Adaptability?