I know that you trust your source very much and I think I know who it is too. I'm not gonna tell you you've been stooped but I will say this.... I have been in touch with a "client" over the past few days who is very knowledgeable about the subject. In any form of entertainment, one of the first things they decide after the concept is the character design, according to my client, this is one of the main ways that info. gets leaked. This is because the company goes through many focus groups and anything of the sort(depends on the company and their goals) to finalize the list(after all it is the most important aspect of things like movies and video games. After much thought, some characters are then green-lit while others stay in the dust. Incenaroar was probably not given the green the light due to this games roster mainly focusing on ballot pics(Incenaroar was absent on the ballot), how they would only go of design concepts and the fact that gen 7 is already over. The difference between him and Greninja was that the frog came out around the same time as X and Y, same with Lucario and DP. It's highly plausible that Incenaroar could be leak bate or something of the like. This also explains why during the ESRB leak Mewtwo was given a ? due to the leaker knowing that he was in the game..... but not in the base-roster.
-Sorry for any spelling errors: Daedulus