Who's Isaac? Isaac is the main character of the game Golden Sun, and an important playable character in the game Golden Sun: The lost age. He's the most representative character of the series. He uses something similar to magic called "psynergy"; he's a user of earth elemental psynergy, and a great swordman.
Why Isaac? Because Camelot, the company making Golden Sun, is a 2nd party to Nintendo; in fact, Nintendo do have the rights for the characters and the music. He would be the representative of a new and fresh franchise, which has never been used in Smash Bros before. Golden Sun has been one of the best selling games ever, so, why should Nintendo ignore it and don't put Isaac into the Brawl?
There's a whole plenty of reasons of why Isaac should be get in Brawl. It would be such a negligence for Nintendo to have dozens of Mario, Pokemon and Zelda characters, and not even one of the best Rpg's ever: Golden Sun. So I'm really looking forward for him to get in; if he didn't, I won't even bother in buying Super Smash Bros Brawl.