-I think we'll see YL in Brawl one way or another. Technically, he is the original Link, but whatever. Although the Celda/Bowser Jr/Ridley package was proven false, I wouldn't count Celda out. He is the official new look for YL. He's in a bunch of games starting with the hit Wind Waker. He goes on to Minish Cap, Four Swords, and is coming out with the WW sequel on DS: Phantom Hourglass. So, I wouldn't count him out. But old-school YL is probably going bye-bye.
-The original 12 are coming back.
-IC are unique, so that's the only reason I think they might stay, they really don't have any other reason of staying in, so they're 50/50.
-Pretty sure Peach is coming back, but not the one we know, I feel an entire new moveset is falling upon her pretty little shoulders.
-Bowser is also 50/50. I wouldn't be surprised if they kept him out just because they couldn't give him a good moveset. His Neutral B and UpB were the only moves that are worthy of just being recognized. His DownB makes no sense since he shares it with a creature 1/100th the size of him[exaggeration, but you get the point] and his ForwardB is just an extended grab or upspike.
-Shiek has a huge fanbase, but mostly because she's really good. 35%
-Falco. big fanbase, but again like Shiek. He's either being replaced by Krystal [NOT Wolf] or granted the honor of being Luigified, proving he has passed The Gauntlet. 50/50
-Zelda. Oh Yea....
-Ganondorf. Probably getting his own moveset. 70%
-Marth is in a unique position. He is the original Lord of Fire Emblem, so that title could give him a spot. But from what we know so far, the castle is PoR. So unless they only add Ike and keep Marth, I'd expect Ike to replace him. 40%
-Roy, Roy, Roy....Oh Boy, he was in for promotion. Now, when characters become popular, they get voted, and when people win votes, they win things, sometimes positions, or a spot on the roster. And how do characters get popular? Promotions baby! Basically depends on how well FE6 did, is my guess.