If Sigurd was to appear in Brawl, then, all three Fire Emblem characters would have blue hair! (lol)
Well, there's something I have to say almost nobody knows; if you look in the musicians section, you'll see something very interesting...
Michiko Naruke Serie Wild Arms
He/she just works for the Wild Arms series, so, what's the point having him/her there? Well, let me tell you something...
http://wii.ign.com/articles/777/777071p1.html
Maybe we'll get to see some Wild Arms character on Brawl? I think most likely not, but it's an incredible coincidence.
Talking about more serious subjects, I just need someone to confirm me that Isaac will appear on Brawl. I need him as a playable character, and the Venus Lighthouse as a stage. Oh, wouldn't it be so wonderful...
By the way, I'm totally against another Mario character. There are a whole bunch of them, and I'm so tired of seeing so many. Sooo, I think Luigi's fine, and Geno and the rest of them should not appear. But that's just my opinion, not based on evidences.
I would SO love Skull Kid, Majora or Oni Link to be in Brawl, although I know it's so unlikely for them to get in. Midna has more chances, of course, and i't wouldn't dissapoint me if she does. Sheik and Ganondorf are definitely going to appear. And... There's one character I just made up, but that I think would be... "Interesting". Instead of Young Link, it would be funny that there was some kind of "Mask Link", being something like Pokemon Trainer; he can transform into a deku, a goron, a zora, a giant, or even in the fierce deity. But that's nog going to happen, I know. What about Kafei? xD
I don't think there's going to be another Metroid character. Seriously. But, if it had to, it would be Ridley without a doubt. I even want him to appear. But he's so huge it would be annoying.
Falco will definitely come back. Everyone loves him; I like him better than Fox. He's the coolest character in all Star Fox series, and one of the main characters. So I think he'll come back. For the third one, even though I'd love to see Wolf brawling, I think it'll be Krystal who comes to fight. I don' t really dislike her, although I would enjoy much more playing as Wolf.
Lucario is not going to appear. Because, you know, there'll be Pikachu, Jigglypuff, probably Mewtwo (I hope they improve him, he was terrible at Melee) and Pokemon Trainer; five characters out of a game would be an abuse.
The Fire Emblem question is the most difficult one. Roy was one of my main characters, I don't want him out, although I know it's most likely to be so. And, for Micaiah... You know, I really like her, I'd love to use her, but I really doubt she will be the one to appear in Brawl. In fact, I even doubt Eliwood will be the one to get in. Sigurd and Roy are most likely to; so, if they cut out Roy, Sigurd will be his replacement. Blue hair to the power!
I like Claus, but I don't really want Ness out of Smash Bros, so I think Lucas and him will be the representatives of their game.
About the second F-Zero character, I'm totally for it.
Well, this is as far as my opinion goes. As I said, it's just what I think, not what will definitely be; if it was, there would be three Golden Sun characters, two Golden Sun stages, and Maxim and Dekar from Lufia. Lol. But I'll be satisfied with just Isaac getting in Brawl.
Great work for your analysis, that's a lot of work you have put into it. Congratulations~