Waluigi has a better chance than daisy. Also, as much as we hate to admit, Tingle does have a very good chance. Infantry and tanks may be possible as part of a bigger Advance Wars character. Kat & Ana are one of the requested characters from Wario ware.
Kat and Ana? I hear more talk of Mona and Ashley (especially Ashley)... Rarely do I hear anyone speak of the Iga Clan duo.
Could and may be playable in the next smash
Ray MkIII (Custom Robo)
Isaac (Golden Sun)
Lil mac (Punch out)
Maybe
Shadow (Sonic) - As a costume of sonic
Samurai Goroh - I think Black Shadow will make it in before him
Lyn (Fire Emblem) - We will get either Roy or a new rep before her. She just does not have a chance.
Saki Amamiya (Sin and Punishment) - He may be popular, but not well known. Also, others are more important than him.
Stafy (Legend of Stafy) - He has a chance because his game is coming to the US.
Waluigi (Mario) - After Bowser Jr., Paper mario and even Daisy, he really has no chance.
No chance
Infantry and Tanks (Nintendo wars)
Barbara (Daigassou)
Dr. Wright
Knuckle Joe (Kirby)
Devil
Andross (Star Fox)
Mr. Resetti (Animal Crossing)
Excitebike
Gray Fox (Metal Gear Solid)
Metroid (Metroid)
Tingle (Legend of Zelda)
Kat & Ana (Wario Ware)
Jeff (Earthbound)
Helirin (Kuru Kuru Kururin)
Jill (Drill Dozer)
Dog (Nintendogs)
Lakitu (Mario)
Hammer Bro (Mario)
I could believe Isaac and Lil Mac, especially if Mac gets enough rep from Punch-Out!! Wii. Ray MK, I'm a little iffy... Then again, I'm just saying that as I know nothing of his series. He'd make for an interesting franchise addition, though, don't get me wrong. We're in need of a few more of those, standalone or otherwise.
Shadow, and possibly even Silver, I could see as future Sonic costumes... That'd be pretty sweet.
I agree that Black Shadow has a wee bit more of a chance getting into SSB4 than Samurai Goroh, as the roster's in need of some serious villain rep, but that's probably just me.
Lyndis would be awesome. She was one of my supported for Brawl... But, it's becoming more and more unlikely, especially if a new Fire Emblem is right around the corner.
Saki... He's an interesting one. He's one of those "Okay-he's-in-the-game-cool" kind of characters you probably wouldn't mind, but not be completely interested in. He has a chance, though. The Ice Climbers got in with little to no support, why not?
Stafy... We may need to see what kind of reception he garners from outside of Japan before we can speculate him getting into a future Smash title playable. (Though, I see he has a chance just because he looks rather similar to a certain pink puffball... Right, Jiggs?)
Out of nearly all Mario reps, Waluigi has one of the slimmest chances. He has a little bit of support, but nothing compared to the likes of Bowser Jr./Shadow Mario and Paper Mario. As for Daisy, she actually appeared in a Mario title that had a plot, whereas Waluigi has yet to make it into any title as a lead villain or character. (Wonder how Rosalina would fair?)