Honestly, I don't see Lucas returning. Although he is one of my favorites. Same with Ike. He may be replaced by Chrom instead.
As for Snake and Sonic, I see Sonic with the higher chance of reappearing. With all the Sonic games for Nintendo consoles plus the exclusives, he's practically a Nintendo character at this point. xD
Others I'm hoping are playable are Ghirahim (Zelda Skyward Sword), Mewtwo (with his new form), and Shulk (Xenoblade).
I have several problems about these suggestions:
- Lucas and Ike first appeared in Smash Bros. as default characters, and based on the fact that all of the default characters from Melee (Bowser, Peach, Zelda, Sheik, and Ice Climbers) made it, then so will Brawl's default characters (Pit, Metaknight, Wario, ZSS, Ike, Pokemon Trainer, Diddy Kong, Lucas, Dedede, Olimar) in this game, as proven by Olimar's return rather than being replaced by Alph, Britney, or Charlie.
- Ghirahim is a one-time Zelda character, which means like Midna, he'll be irrelevant to the series in the next Zelda title. The only reason why Sheik got in was because she's technically Zelda and is used as part of Zelda's play style to make her stand out from the other fighters.
- Just because Chrom is recent doesn't mean he's an automatic shoe-in. This is not the reason why Roy and Ike were chosen in the previous titles (Roy was picked by Sakurai because his fire power made him stood out from Marth, and Ike was suggested by Intelligent System when Sakurai was looking for a new FE rep). Besides, Roy was originally meant to come back in Brawl to co-exist with Marth and Ike.