First going down the list of Gen 6 Pokemon we can probably rule out any Pokemon that is pair with another Pokemon, such as the version exclusives Clauncher, Skrelp, Swirlix and Sprizee as well as the starter evolutions since I doubt that they would reveal one without reveling the other(s).
Next lets rule out those already with a evolutionary family, (aside from the starters) we have Pancham, Pangoro, Fletchling, Talonflame, Skiddo, Gogoat, Scatterbug, Spewpa, Vivillon, Litleo, Pyroar, Inkay, Malamar, Tyrunt, Tyrantrum, Amaura and Aurorus.
Non of this Pokemon look like they may have a branched evolution.
Now we have 8 Pokemon to choose from.
Helioptile, Noivern Flabebe, Honedge, Dedenne, Bunnelby, Furfrou and Meowstic.
First lets Eliminate Noivern because how would you evolve this thing? It will probably ether have a pre-evolution or not evolve at all.
Next lets eliminate Dedenne, this generation's version of Pikachu chances are like it's predecessors Plusle, Minun, Pachirisu and Emolga it will not evolve.
Next Furfrou seems like more of a gimmick Pokemon then anything else and most if not all gimmick Pokemon don't evolve.
So now we have 5 Pokemon, Helioptile, Flabebe, Honedge, Bunnelby and Meowstic, now I don't see allot of people asking to see any of their evolutions (although I would mind seeing Meowstic's or Honedge's if they have one) and the reveal would seem under whelming.
So who?
What about Orotto? in a recent video a Sudowoodo was seen in a hoard of Orotto, could this be a Sudowoodo evolution? I doubt it, said video featured a Flareon attacking the Orotto hoard with a fire attack and dealing super effective damage so unless it completely changes it's type it probably isn't a Sudowoodo evolution, plus since when have the final evolutions of three stage evolutionary families found in the wild?
Now we've gone through all non legendary Pokemon reveled so far, except one, Sylveon, I predict that the new Pokemon reveled will be another Eeveelution, why because since Generation I two new Eeveelutions have been introduced in every even numbered generation so it seems odd that they would only introduce one for Generation VI, the next question is what type will it be?
Well every time a group of Eeveelutions comes up in the National Pokedex the first one on the list is always weak against the second, (The Water-Type Vaporeon is followed by the Electric-Type Jolteon, The Psychic-Type Espeon is followed by the Dark-Type Umbreon, and the Grass-Type Leafeon is followed by the Ice-Type Glaceon) so this narrows down the possibilities as the Fairy-Type is weak against Poison and Steel type, but Sylveon could be second in order giving us three more possibilities Fighting and Dragon.
Another thing to consider is that all of the previous Eeveelutions were members of the 8 special types and while the Fairy type doesn't belong to either the Special or the Physical Types due to being introduced after Special and Physical attack were type exclusive, it can be considered the 9th Special Type to even things out with the 9 Physical Types, now given the 7 Eeveeultion types plus Sylveon as all being Special Types it would make since that the new Eeveelution's type will be from the last remaining Special Type.
My prediction for the new Pokemon is a Dragon-Type Eeveelution.
