I don't think he's going to do that. He's just interfering with the Trophy world. I see no indications that he can/will break the fourth wall.
I think he's just going to be the leader of whatever the subspace emmisary is.
Good point. In my defense, breaking the fourth wall seems to be a theme of Smash Bros. You know, like how during Hand Battles, Final Destination's background decays into wireframe, that sort of thing. Indeed, the hands themselves are implied to be avatars of the player/game creators.
However, I have noticed that the art style of Brawl is becoming steadily more realistic (relatively speaking); the Break the Target levels are no longer polygonal in appearance, and the Battlefield is now a Mediterranean ruin, not a floating platform in cyberspace. So it's possible that they're abandoning this technique for a Kingdom Hearts style multiverse.
Classic mode will hopefully continue with the Master Hands, wireframe-style mass opponents so on and so forth.
The Subspace Emissary is a whole new story, however, literally and figuratively. I see four possibilities:
1. They play it straight, Kingdom Hearts style. They create a multiverse with self-contained laws to explain travel between places in the multiverse.
2. They go old-school, with battles in cyberspace where the battlefield decays into wireframes, that sort of thing.
3. They don't truly break the fourth wall, but their are vague hints. At most, things like "What A button?" by the character, with a response of "interdimensional beings will understand." Nobody ingame explicitly realizes what's going on, but they notice somethings amiss.
4. The Secret Ending potential. You play through the Emissary on easy at a leisurely pace, everything is played straight. But when you charge through it on hard and crush all who stand before, you're in for a surprise...