I'm going to assume that, as with each set of Eeveelutions, this will be a pair with one having type advantage over the other but stats to counterbalance the matchup. Since the games are X and Y, I'm also going to assume that it'll be a gender-based evolution.
My assumption is that Ninfia is a flying type as all the other Eeveelutions have their fur tinted the color of their type. (For this logic, I'm assuming that if Nimfia were a Bug type, it'd be tinted lime green.) Further, I think it the new Eeveelutions will be game-specific, with this one set for X because it appears more feminine. The Y pair is likely going to be Bug, Fighting, or Rock and have a more masculine appearance. Since Ninfia's dimensions don't lend themselves to a bulky pokemon, I'm going to guess it's going to be high speed, good attack or good special attack.
Therefore, the remaining Eeveelution will likely be more defensive in nature. I'm going to venture a guess at high defense, good attack, awful speed. This might indicate Rock because that matches the generic Rock stat distribution.