Alright. I predicted that (Roy, Pichu, Doctor Mario, Falco, ICs, GandW, Sheik, Jiggs and Luigi will be taken out). That brings the roster from 26 to 17. I then guess that there would be 15 new characters which would bring Brawl's roster up to 32.
But I remember reading on a translation that Sakurai may reveal every character before the game comes out because people will find out anyways.
So let us say that he stays with his word and does this. We have 13 revealed characters on the website. We have about 4 months exactly left until the release. (4 weeks in 4 months so 16 weeks).
Each week a character is revealed. Let us say he sticks with that pattern.
16 plus 13 is 29.
But I used many assumptions to get to that number, but it is not to far off from my predicted number of 32.
Firstly, I didn't realize about the one character a week deal. I knew it was pretty much once a week, but it didn't dawn on me how many weeks left. And seriously, Luigi? C'mon man, that's a stretch. And people don't understand that Jigglypuff was put in the game after she'd already been cut, just to add a number to the roster, showing Sakurai really doesn't care much for her.
Now, about the "16 plus 13 is 29" business. Of the Melee roster, 9 movesets(characters) are left to be confirmed, without clones:
-Luigi, C Falcon, Jiggs, Ness, IC, Sheik, Mewtwo, Peach, G&W.
*Remember that C Falcon, Luigi, and Ness count as one of the weekly character updates, as they haven't been shown yet.*
If all of the above characters return, that only leaves 7 slots for "Newcomers" such as Pit and Wario. Cut G&W, Mewtwo, and Sheik. Now you've got 10 slots for Newcomers. Sounds great if you add them to the 5 Newcomers from the trailers, however we have yet to get a Dojo update for Meta-Knight, and Snake if Sakurai is updating hidden characters. Cut your Newcomer list now to 8-9. From this point on, we are only getting 8-9 Newcomers we don't know yet as of the week of July 22-28, 2007.
Cut 1-2 more off for the Third Party characters, leaving us with 6-8 Nintendo Newcomers.
This is seeming more and more similar to Melee, instead the excuse is that he's going for "quality over quantity" instead of the "running out of time" used for Melee.
Again, this is on conservative scale based on popular belief. I find it rather realistic to be honest. It doesn't sound like too little that it won't be interesting and not too much that at that point the characters might seem to just be being thrown together.