Trust me I don't want it to be everything, but just like when mallow was revealed, I admitted the concept art as real. Everything was datamined. So either that is all the pokemon, or Nintendo purposely wanted the game to be datamined and left random things out.
I am not saying it happened but that would be pretty funny if they did purposely hid some things and not other things, in a way they would have learned from the ORAS demo lol well either the announcement next week or the actual game release will shed light on everything. If things were hidden or not I still think most of the new pokemon this generation had awesome designs for the majority so I cannot wait to try my teams I have in my mind. The only bummer is just the amount of single stage pokemon seems a bit excessive, which I can see a lot of backlash from fans, hopefully the single stage pokemon have stats to make them in some way competitive.