That leak is believeable, tho I'd rather it not be entirely true... mostly for personal reasons of simply not caring about any of those characters. But I can't argue that they all would be surprising and most of them are arguably very iconic.
Call Steve a meme or whatever, but Minecraft has been maybe the most stupid popular game of the last decade. One might call it the game of the decade. I myself have enjoyed it and I bet most of us have at some point. Although, like most of us I imagine I'm not alone in feeling like that's a wasted spot for DLC. But I'm not from the generation born in the last 20 years. There's absolutely no doubt Minecraft is huge and iconic at this point though and Smash representation of some kind is probably as deserving as anything else third party at this point.
And as for Doomguy? Seems ill fitting to me, and though I enjoyed the games, his character was never more than the implied violent nature seen in his actions. But, like MC, Doom is THE first person shooter. If you were to name a game that represented the genre and really started it.. most people would name Doom. The game is legendary really, and it's protag is part of that legacy obviously. Him in Smash as an icon of gaming is not ill fitting. Just, in my own opinion... I'd prefer something else.
As for the others... I mean, Ninja Gaiden has long history on Nintendo back in the early days. Getting representation for that series would be no different than Castlevania getting representation... though I'd say Castlevania was always more "iconic" as part of the Nintendo family in the early days. And DQ is for Japan mainly. It's huge there and it's a franchise that's been around forever that's recently been very friendly with Nintendo again I guess. It also makes some sense.
Nothing is terribly wrong with these inclusions if the leak is true. Only thing wrong is that I don't care about any of it, heh... I can appreciate the significance though and I'll probably get every DLC character whoever they might be anyways, and I will play every one of them, no doubt. Just without the significant level of love and joy I would if a character I really cared about was one of them.
unfortunately we lack the bandwagoning power of the other characters, we've managed 167 followers on the support twitter however. Though fortunately for us, the mountains we have to surmount is much less than Isaac or Geno try as they might I don't think they'll ever have new games. K Rool is lucky that he's in Donkey Kong, a beloved and more importantly active franchise. And He had MANY more fans than any of the other characters, barring Ridley. It's fascinating how much people went behind Ridley, The way it looked there were more people talking about Ridley than there were people who bought metroid games in general. Regardless twitter conversation is good, but the letter campaign I suspect is better. Even though she's bound to show up in the next SF game we need more passion in the community to help convince them to make her playable. Her vocal popularity really vanished post 2015, people have forgotten her and push in favor of other characters simply so they can have what they perceive as a chance of winning. Krystal really does have potential for an underdog victory. I was convinced of this during speculation pre-ultimate and she made it to assist level, something many people would have said is ridiculous for her. But if we don't show enough support, they may think an AT really is enough. I know alot of people don't have her as the first option, but for me she's the only character i've wanted in smash. So if we can have others make her a priority and start writing letters to their local nintendo branch, asking for her for smash to promote her to playable fighter. Throw in having her return to Star Fox too, doubt that's necessary but can't hurt.
Btw, in response to the concern about Krystal's popularity that Gagnetar and others were discussing like over a week ago now... the trouble for Krystal is that the most exposure she's gotten in the last decade is right now in Smash as an AT. It's something for sure, but it's not necessarily gonna attract new fans in the numbers you might expect from a whole new Star Fox game with refreshed and fleshed out character portrayals. What Krystal desperately wants is another chance to have a good character portrayal in her own game. It's what I'm left wanting, with only the faintest glimmer of hope she'll get more representation in this Smash beyond this assist trophy. And really, I don't know that I even want that "now". I'm content with the assist trophy and am glad we even got that much considering how long it's been since Krystal was on the radar. That was our doing in part. I don't necessarily need to ask more of Smash before I ask for Nintendo to bring her back to her own franchise and in a really loving way. There's no doubt that the most that can be done for her popularity is that. New eyes on a new Krystal in a new Star Fox, done right... nothing can compare to that impact. So that's what I hope for. Smash is secondary and her representation could be the outcome that bigger more impactful desire.