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
Paper mario has plenty of stuff to make a good spirit board still of course, I just think logically nintendo would have held off those paper mario the origami king spirits to be part of his board if he was coming. Its more about the timing, being during this dlc, rather than the fact he has spirits in the game at all.
ARMS had spirits already but again those were base game and likely before the second fighters pass was decided, these new origami king spirits of course are during the 2nd fighters pass so no reason to add them now instead of waiting and adding them with paper mario if he was coming.