C'mon guys! I'm tired of Light type discussion. Really tired.
GameFreak has had so many opportunities to introduce Light type - Espeon as counterpart of Dark-type Umbreon, Cresselia as Moonlight Pokemon and counterpart of Dark-type Darkrai, Arceus as deity of the Pokemon World, and as Metalizard said people speculated on Dragon/Light type Reshiram as counterpart of a Dragon/Dark Zekrom - till now they never did.
There was only one expansion of type chart back in GenII (probably for balancing issues) and since then GameFreak never touched it. The reason: They don't see a need to add new types.
Of cource I can't exclude the possibility of new types in future, but for now it's very likely that Ninfia will be classified with an already existing type.
So as Ninfia is an Eeveelution we can assume it is a pure type and we can exlude the 7 existing types of Eeveelutions, leaving Normal, Fight, Flying, Poison, Ground, Rock, Bug, Ghost, Steel and Dragon.
Right at the beginning I'd like to rule out Fight, Poison, Ground, Rock, Bug, Ghost and Steel for obvious reaons.
Allthough I read arguments for Fight (ribbons as weapons) and Bug (butterfly-shaped bows), Ninfia has nothing of a brave Fighter nor it resembles any insect-like species.
I would consider Flying, Normal and Dragon as possible types
FLYING:
As I wrote in a previous post Ninfia makes me think of a kite. Original simple-constructed kites often have ribbons and bows on their string. Especially the central screenshot at top of the CoroCoro page shows that the ribbons blow down Ninfia like flapping in the wind. Of course it has no wings but it might otherwise be airborne. I guess a trailer of the short movie showing Ninfia in motion will either back or scrap this.
NORMAL:
This guess is based on the fact that most cute-looking, girly and pink Pokemon (especially Skitty, but also others like Clefairy and Jigglypuff) are Normal type. Also it's name if really derived from nymph (which is greek for bride or young woman) would back this. However this would prompt the question if Ninfia has a male looking counterpart. The biggest counterargument against Normal is simply: It's Eevee, the Evolution Pokemon that is said to adapt to each enviroment by mutation. A normal type Eeveelution would be odd as this non-anomaly is already portrayed by Eevee itself.
DRAGON:
I know Ninfia doesn't look like a dragon at all but there are two (maybe weaker) arguments for it being Dragon Type. First: It's the only former special type without Eeveelution which isn't a strong point by itself. But I like to repeat my kite argument that I used for backing up a Flying Type. The words for "kite" and "dragon" are identical in many European languages (e.g. Norwegian, German, Swedish). Usually I won't give a sh.. about this argument as Japanese game developers might not be aware of this linguistic fact. But as the new region is based on France/Europe and the legendary Pokemon are taken from Norse mythology it's worth to mention it. And remeber: Kingdra and Flygon aren't based on Dragons either, but people named the animals they are based on seadragon and dragonfly, respectively, so this might be an argument for Dragon type.
1 EEVEELUTION OR 2:
Since GenI all Eeveelutions were released as a pair of counterparts: Espeon(sunlight/day) vs. Umbreon (moonlight/night) and Leafeon (moderate forest, species-rich environment) vs. Glaceon (extreme tundra, hostile to life). So if there is a counterpart to Ninfia it might pick up the gender theme and will probably look rather male, IMO a Fight type would be appropriate. If Ninfia is Flying type, a Ground type counterpart would make sense, too (habitat air vs. habitat ground).
If Ninfia is a loner, Normal and Dragon would make more sense as they emphasize it's uniqueness.
tl,dr:
I rule out a new type and several other types, leaving Flying, Normal and Dragon as Ninfia's possible types. If we get another Eeveelution it might be a male-looking Fight or Ground counterpart of cute female-looking Flying type Ninfia. If Ninfia is a loner I go for Normal (with a minor chance of Dragon).
EDIT: English name SYLVEON strongly supports theory of Flying type as Sylphs are mythological AIR SPIRITS.