That would be a boner softener. Like, anti-Viagra. Why would they create a normal Eeveelution? That's so boring.
Plus, they're keeping the typing a secret. Are we all supposed to get excited when they reveal that this thing is a *drum roll* ...Normal type? Point being, if it was normal, they would have just said it was normal instead of hiding it.
Eeveelutions are full embodiments of their types. You can TELL Flareon is fire. You can TELL Espeon is Psychic. You can TELL Glaceon is ice, Vaporeon is water, Leafeon is grass. That's the point of Eeveelutions; they have nothing defining them other than they're types. But when we all see this new Eeveelution, we have no idea what we're looking at. It looks as though it may have a little flying influence, but it doesn't fully embody flying like the other Eeveelutions embody their types. There is no strong indication by its artwork that screams "I CAN &%$#ING FLY." And Game Freak knows we can't tell what it is, or else they would have listed its type as "Flying" instead of "???". They're keeping a secret.
But why? Why would they show us an Eeveelution, but keep ambiguous the feature that DEFINES it? Why would they make an Eeveelution that does not seem to fully embody any of the types we know and love?
My guess is that its because its NOT a type we know. It's a new type. That's why we can't recognize its typing by looking at it. That's why they're keeping its typing a secret. Because the unveiling of this new type is an unveiling for another day.
So what could this type be? Well, I hate to revisit what has been falsely speculated in generations past, but this seems to be a Light type. Or in Japan, "Pure" or something along those lines, since the Dark type translates to "Evil" type in Japan. This Eeveelution fully embodies "Pure" in that it looks friendly and welcoming; its bows give it a feminine, almost childish feel of innocence. Its colors are limited to mild, calm colors rather than brighter, more violent colors, which extend to a spectrum at the tips of the ribbons flowing from its bows. The spectrum may be a nod toward the concept of light.
If this is true, and a light type is brought to existence, then it is likely that Xerneas is a Light type as well, as an opposition to Yveltal's likely Dark type. Light and Dark; Good and Evil. Note that "Evil" is already hinted at in Yveltal's name, so this is likely a theme. And of course, Xerneas looks very heroic and bodes well the appearence of "Good", and also embodies light (look at its antlers).
If a light type is created, its likely that some Pokémon from past generations will adopt the type as well. I'm looking at you, Chansey.