The veteran Pokes we already have; Jiggles 'n Pika; are stayin'. That's obvious and incontestable. Red and Lucario, however, there's no definite chance either way. My take on Red is that they definitely won't give 'em the ban hammer. He's the original iconic protagonist. Despite DP coming out right before Brawl, Red still got in over Lucas and Dawn/their manga counterparts or anyone else from Gen 4. Furthermore, despite bein' one character he has three 'mons. Givin' him the axe means three characters dropped. Sakurai won't do that I don't think. Let's not forget Red is the only human representin' the Pokemon series. His odds of returnin' are very good IMO.
Lucario's however, I'm not as positive of... but nor am I negative. Lucario is a vastly popular 'mon in both the Pokecommunity and Smash community who wholly represents Generation 4. Mewtwo was the same way for Generation 1 back in Melee and look what happened when he got removed, people right-flipped the **** out over it. Lucario is definitely the most likely candidate t' be removed, but I don't think it'l happen as it'd be both a very unpopular decision, and one I don't think Sakurai would likely make anyways. He's received nothin' but flack from removin' even clones... do ya really think he's gonna remove a unique fighter?
Lastly, Pokemon definitely won't receive more than one 'mon. If Smash 4 came out this year, it'd probably be Zoroark... but as MR said, we're one Generation late. Smash 4 ain't comin' out 'til long after XY's release. Furthermore, Zoroark's popularity isn't on Lucario's level despite bein' representative of Gen 5 and gettin' it's own movie... a movie which is now old in the face'a other Pokemovies released over the past few years. Zoroark isn't gettin' in, period. There's almost no chance it'l happen.
As for Mewtwo, it's hard t' say. It all depends on Sakurai's decision in regards to the Pokenewcomer: return Mewtwo as the fans want, or add in the Gen 6 representative which hasn't been revealed yet... Mewtwo is, without a doubt, the most popular Poke in Smash. No, Pikachu really ain't. The electric mouse is iconic, but remember that popularity in the Smash community is moar important than popularity amongst people who still play the Pocket Monsters. People who don't care for modern 'mons anymore still oft have some nostalgia for Mewtwo. Whether it'l get in as it's new form or said new form will be it's final smash, I don't know. But Mewtwo's chances of returning are pretty much guaranteed if Sakurai decides t' not take a Gen 6 Poke.
I'm relatively confident with my following vote.
'Course, the latter two certainly can't be predicted with the utmost certainty, but I'd still be willin' to bet on it.