Dude this is the equvilent to asking for Captain Falcon to be in Wipe Out it will never happen because 1st party companies don't let other 1st party companies use their stuff, if I remember correctly, when Marvel Ultimate Alliance was first coming out Link and Samus were originally going to be guests for the Wii version but the way Activision showed it they were being played on the PS2 version, Nintendo didn't like the look of that and decided to strip Activision of those rights.
I can't see Nintendo characters being in this game. Maybe a 3rd party character that is primarily on Nintendo but not an official "Nintendo Character" For example there has been plenty of Sonic the Hedgehog games on the Nintendo and Playstation so I could see him being in the mix but not somebody like Kirby.
Also, about Snake, if you didn't know, Kojima asked Nintendo to add Snake to the roster for he is a fan of the Smash series. I doubt he'd want Snake in both games. And you guys already have Raiden. At least.
And...I can think of Nintendo characters that would at least fit the tone of the game. Fox McCloud of Star Fox comes to mind.
Probably a better change of getting Mickey Zouave than a znintendo character. Nintendo doesn't license out their Izp, that is the only thing they have that sells their hardware. the only way it would happen is if they get out of the hardware business, a similar to the way Sega is now (very unlikely to happen).