I doubt they would put Mega Man or Bomberman in the next Smash Bros. Mega Man might (never played the series, so just a guess) have enough moves to fill up the move controls(B-up, A- Left) But what would Bomberman have? Bombs. Thats it. there's three characters with bombs already. (Toon)Link and Snake. Snake and Sonic will make a return. I know Sonic will, since he's the fastest character in the game. I'm hoping Shadow will be in the next one. And dont anybody say they'll play exactly the same, because there's Ness and Lucas, Mario and Luigi and Fox, Falco and Wolf. The only difference is either one attack, or the attack is a little different, like Fox/Falco/Wolf's blaster and PK Fire and PK Thunder. Shadow would have Chaos Spear as his B-attack, and all of his awesome skills. He's already an Assist Trophy, so that means Nintendo was thinking about making him a playable Character, but only put Sonic in and made him an Assist Trophy. Tails would most likely come in next, or Knuckles.
They better keep my Lucario in the game. Put Mewtwo back in too. They're basically the same. Only difference is Mewtwo's just a light-weight. Gets thrown off easy. Final Smashes better stay.
I'm thinking that in the 5th one, if it gets that far, they'll have every character that was ever a usable character back in. And every stage that was in the Smash Bros series would be back. I love Dream Land. On the Original Smash Bros, it was my favorite stage.