Oy, we've really gone from discussing what might in store for Smash Bros. as far as new characters (Outlook Not So Good since Duck Hunt Dog is getting a debut trailer more than a month after people discovered his existance), but considering that hyping Duck Hunt Dog as a newcomer won't be a good idea, I'll just throw in my two cents about the moral alignment spiel.
First off... Hades of Medusa?
In my opinion, I guess that although he is the true villain of Kid Icarus series, he's too new to be known as the main villain.
If I was to choose a villain from Kid Icarus, that'll be Medusa, because she was a main villain from the first Kid Icarus before Hades, and although she had lesser roles on the recent ones and might not be so popular than I thought, she was still important as part of the main key person of the series. But there's one point...if the Smash 4 takes place after KI:U, then I do understand why Medusa nor Hades were not chosen...
I can understand that argument for Hades, but my argument against that is that he was too new a villain, while Medusa, in spite of her reduced stature, remained vital in the Kid Icarus mythos. Plus... I feel Medusa doesn't get the respect she deserves, especially since she was the only character I could like in Uprising since she was honest about everything and wasn't wasting time cracking jokes and trying to be funny (I don't play as any of the KI characters unless I need a punching bag). Also, how can you go wrong being the only
female playable villian in Smash Bros.?
Second... Who Goes First (aka Golden Sun talky time!)
Well, Palutena is far more popular regardless. Also, Dark Pit was a last minute addition to the roster anyway. Medusa was probably the more likely villain if one was chosen due to her key status. It's like choosing, say, Grodus over Bowser.(just imagine Grodus was introduced before Bowser was before Melee was created for the purpose of this argument) Or, if you will, Majora over Ganondorf, since he was more recent.
From what I've noticed, the villain choices(the first one shown) is the main one first seen or more important, not the latest one seen. Just like the main hero of a series would be the first specifically from that series. I.E. Let's say they did a Shining Force representative. It's going to likely be Max since he's the first hero of the series as a whole. Shining in the Darkness is... odd. I can't even remember if it has a canon hero. Same with Isaac in Golden Sun. Felix existed around that time too, yet he doesn't much appear. I don't know if he had even a single appearance in Brawl. Maybe a Sticker or Trophy? It's clear Isaac was the main hero. It's made more blatant he's the main hero at the end of the second game, although that's a spoiler-based reason. Another funny example would be choosing Silver over Sonic just based upon the Sonic series itself. He's the latest hero, and even could bring a highly unique moveset(even if it could have a move or two copied from Mewtwo potentially. ...Somehow should make a hack of him using Project M Mewtwo, heh). It's obvious who was chosen, for more than one reason.
Basically, when it comes to Heroes, the first main one of the basic series represented will show up. And sometimes their sidekick(s).
For villains, it'll be the most viable and most notable first. Wolf is both of these, as he's far easier to make a moveset out of than Andross, and can still be considered a villain depending the particular game.
First off, Golden Sun didn't get any stickers in spite of having actual character artwork (as opposed to MOTHER 3, which was just standing sprites for the characters instead of clay models), and Isaac was the only trophy (though unlike most, his artwork and actual trophy are different from each other). However, Isaac is established by the Golden Sun canon as the true hero of the series, and while I like Felix more, his role in the series was merely to be the guy who eventually reveals to Isaac the truth, however unpretty it is, and also show that he wasn't a bad guy, but rather a guy who had to caravan with a pair (or trio in the case of Forever Unfought adversary Alex/Arcanus) of complete a-holes. So, if Golden Sun gets its long-overdue represnative in the Wii U (unlikely) or future DLC (kinda likely), it'll just be Isaac, and that'll probably be how future installments will focus on Golden Sun's involvement.
That's how a newcomer for a franchise shows up for their universe... they have to be the central hero, followed by their sidekicks. In order for a villain to appear, the heroes have to appear first, and in the search of new fighters, the villains would be considered. But, a wrench can be thrown in if there's a new hero that shows up in this timeline... which unfortunately happened in the case of Dark Pit (and calling him a "hero" is the nicest thing I'll ever say about him... he's a Nominal Hero at best), though we can safely argue that his inclusion was A) he's a clone and B) he was a Sakurai creation.
Third... Where Does Mewtwo & Wario fit in the Greal Moral Alignment Debate?
Mewtwo is an ambiguous case, considering the movies, the TV show, and the games often contradict themselves. For example, in the anime, the most iconic Drapion is used by Pokemon Hunter J, the most ruthless character in show history, is presented as evil, but in the HeartGold/SoulSilver manga (where the villains make J look tame), the hero has a Drapion, and it's a good Pokemon. The difference lies primarily on who uses the Pokemon that is a reflection of the Pokemon's mentality or morality, since they reflect on their trainer for support. Of course, in Smash Bros., they liked to emphasize that he is the Savage Pokemon, and one who liked to mock in the Japanese version of Melee, so there is that part of the argument.
As for Wario... he's an anti-hero. He does good deeds, but that's because there's money to be had, or the deed was accidental. That's why I felt the ending of Shake It! was so fitting for him. In Brawl's Subspace Emissary, his villainy is largely because it's the side where there's profit, and it's more fun, while Bowser & Ganondorf are part due to the fact that they are more evil.
Now that I've said this, hopefully we can focus on talking about who might be playable as opposed to just their orientation.