I think the biggest point against DLC isn't Sakurai's statement, but from Takashi Aoyama who said (from the Wired blog) "The add-on contents for disc games would be purchased within the game"
Unless someone with a japanese or other copy of the game can tell me that there is a "Look for Updates," "Update," "Download," or "Give me more characters" button in the game somewhere already, I saying it's not going to happen. In order to update a disc game in such fashion, it seems that it has to able to recieve such an update to begin with.
I still think DLC or expansion discs are a possibility. At the earliest, it'll happen after Europe, Australia, and New Zealand get the game.
I bring this up because I could see expansion discs as a possibility, as Koei has made some pretty good money off of the Dynasty Warriors series in this fashion. However, I find it highly unlikely.
The biggest nail in this coffin, however, is that Sora is
not a big company that has nothing better to do than make more Smash Bros content. As Sakurai stated several times, Sora is really only two people and the rest of the team goes in and out as they are required. Because of that, you're not going to this team sitting around monitoring people's responses and planning their next big Smash move. Chances are, the team no longer exsists at this point.
Sure Nintendo could hire people to do it themselves, but they didn't work on the first project, and likely wouldn't be able to balance it the way Sakurai or the rest of the team would.
Also, the question is, would you be willing to 'pay' for these? If they introduce such content, you will likely have to pay for it, which mean that Brawl's online experience could suddenly fall under the 'pay-to-play' category. At which point, I would hate it, because I'm not willing to spend a monthly fee just to get my online Smash fix.
[/end rant mode]
I don't mean to rant, but as much as I'd like to see other characters included in the game somehow, I'm starting to think DLC could do more harm than good at this juncture.