Phoenix Wright would be, if anything, an Assist Trophy. He would appear next to whoever summoned him, and when they're attacked he'd shout "OBJECTION!", graphic and all, and knock the aggressor right off the screen.
I think Mega Man would be the most likely candidate for being the next third-party Brawler, maybe followed by Simon Belmont as both third-party and retro-brawler. And I'll go way out on a limb and say I'd like to have Wolf Link in the game. I'd also like to see Gannondorf and/or Captain Falcon return. I fantasize about grabbing people and blowing them up.
Latest news: Wario's Final Smash transforms him into Wario-Man. I'd have to say, I wasn't expecting that. The first Brawl trailer suggested it'd be a nuclear fart attack. Now he does a mode-change. I'm not certain if I'm disappointed, but I've definitely got that "WTF" feeling. Guess they've done their job, then. Although, with that mask, I could swear he was supposed to be the Purple Wind.
Coincidentally, I knew a guy in a Sonic forum who had a "Purple Fog" gimmick.