I want to point out something regarding Vergeben/Hitagi and their credible leaks.
The way I understand it, the aforementioned leakers are not the ones with access to the information being leaked. They are merely mouthpieces. This is clearly seen when looking at the 7th Gen Pokemon rep and its identity. IIRC (and I'm going to paraphrase here), Vergeben said that he knew it wasn't certain pokes, but only recently revealed that it was Incineroar after getting enough confirmation from his sources.
Why do I bring this up? Because sometimes, even though there is a lot of true and credible info coming from a certain source, the reality is that it's not just one source: it's multiple. And since there are multiple people feeding Verge and Hitagi their info, it's quite possible that some of the sources, and by association the info are wrong. I'm not saying that they aren't credible and that the info isn't credible. I'm saying that it's possible that SOME of the info were being told could be incorrect.
Am example to further illustrate my point. IIRC, when Pokemon SuMo Alolan forms were leaked, we got news that (forgive me if I get one or two wrong) Ninetales, Golem, Sandslash, and Arcanine would all be getting new forms. After the leaker got told he/she was full of crap, lo and behold we got Alolan forms of Golem, Sandslash, and Ninetales. So people, after now trusting the leak, sat and waited for the news of Arcanine to come. Here we are, far past the release of the game and Alolan Arcanine still does not exist.
So what are my personal thoughts on these leaks? I think Ken and Steve are definitely in. I also think we'll get another echo in the form of Shadow (Ken by himself as the last echo seems really weird to me). I can actually see the SE rep being the last character (which has got to be Geno, only because given Sakurai and Geno's history, I can't reasonably see Sora or anyone else being that character). I've personally always been iffy about a Pokemon making it into the base roster. I know we've always had one added and all the jazz, but I just feel it goes against the theme (if you will) of this game. This game is about bringing in fan favorites. If you look at consolidated polls (as they are one of our few more concrete sources of data), the first Pokemon rep to show up was after spot 40, and it was Pichu IIRC.
Incineroar being one of the first DLC makes more sense to me. SuMo was released after the roster was probably finalized, so I could see Sakurai adding him to the game once the Pokemon Company felt more confident in its popularity instead of hoping another Greninja situation would play out well for them. This way, Incineroar could offered as free or criteria-locked DLC and would viewed as a bonus character rather than a "it took X character's spot" kind of deal.
Edit: spelling. (It's late where I'm at, so forgive me if you find anymore.)