My list of the ones i just think should be added is that one here.
Mario Series - Waluigi; Toad
StarFox Series - Wolf O'Donnell; Leon Powalski
Metroid Series - Ridley
F-Zero Series - Black Shadow; Samurai Goroh
DK Series - King k. Rool; Diddy Kong
Zelda - Majora's Skull Kid
-Third Party
Sonic and Tails (Sega) (Sonic Series)
Banjo & Kazooie and Gruntilda (Rareware) (Banjo-Kazooie Series)
Conker (Rareware)(Conker series)
-Confirmed
Wario
Snake
Pit
Meta-Knight
Zero Suit Samus (I will only like that if she be a transfomation like Zelda/Shiek)
Sakurai said he is gonna remove some characters from the last game. Well, i believe the ones should be removed are: Mr. Game e Watch, Dr. Mario, Jigglypuff, Pichu, Young Link and Ice Climbers.
Rumours in the Net are saying he confirmed the participation of Cel Link (WW), Bowser. Jr and Ridley replacing Young Link, Mr.Game & Watch and the Ice Climbers. Nobody knows if that is really true however. Hope the Cel Link it's not, i don't see any smart thing on replacing a link for another one. The other 2 i liked, specially Ridley. He roks! But as i said, it's rumours. Majora's Skull Kid will be much more rlz replacing the Young link! =P
Total: 40 characters like Sakurai said will have (Around that amount, here we have 40 if you get the last game characters except the 6 i said + Confirmed + the ones i said + Third Party + Bowser Jr from the rumours)
1.Bowser
2.Captain Falcon
3.DK
4.Falco
5.Fox
6.Ganondorf
7.Kirby
8.Link
9.Luigi
10.Mario
11.Marth
12.Mewtwo
13.Ness
14.Peach
15.Pikachu
16.Roy
17.Samus
18.Yoshi
19.Zelda/Sheik
20.Wario
21.Snake
22.Pit
23.Meta-Knight
24.ZS Samus
25.Waluigi
26.Toad
27.Wolf O'Donnell
28.Leon Powalski
29.Ridley
30.Black Shadow
31.Samurai Goroh
32.King K. Rool
33.Diddy Kong
34.Majora's Skull Kid
35.Sonic
36.Tails
37.Banjo & Kazooie
38.Gruntilda
39.Conker
40.Bowser Jr