I wouldn't say
probably, but he is one newcomer who I believe has the highest chances personally.
Like, other characters are mostly just wishful thinking (I'm sorry Dillon, Ray-01...) but with the success of Punch-Out!! Wii as well as Sakurai's fetish for classic characters, its a fairly reasonable prediction.
Much better than Villager, Mega Man AND Wii Fit Trainer, that's for sure.
One thing though that might jeopardize it though is this, coming from the Wikipedia article:
"The inclusion of
Donkey Kong was a suggestion from an employee of
Nintendo of America, and Tanabe also wished to include
Princess Peach, but that idea was abandoned because of the issue of violence towards women."
Which makes you wonder if that extends to Smash Bros. Maybe because it's boxing it's "too real" compared to the goofiness of Smash Bros? I dunno.