So....
This may be a deathtrap.... But I'm going to do it anyways!
Just a few thoughts on several of the newcomers / returnees.
[collapse="My thoughts on several newcomers / returnees."]
Mewtwo: Possibly the most likely character out of this list. Veteran. Importance. Popular around the world. Everything is perfectly aligned for Mewtwo to make his return. The Pokemon Company would have to do some MAJOR interfering (and stupid interfering) for him to be excluded.
Roy: A bit trickier than the other likely returnee, Mewtwo. FE characters are very difficuly to predict, but I think it's a lot simpler, than we think. I personally think Roy is dependant on what Sakurai views as most important. If Sakurai thinks fan demand and veteran status is most important, than Roy is the way to go.
Dr. Mario: A lot more likely than people think, methinks. Doc was planned for Brawl at one point. I think he actually has a decent chance of being the fifth Mario character. Again, I think it depends on what Sakurai thinks is most important. If Sakurai thinks veteran status is most important, I can see Doc getting in over Mario newcomers. It's possible that we could get him as an alt costume though. Depends on whether Sakurai's thought on "fireballs =/= pills" has changed or not.
Young Link: Not happening. At least, not with Toon Link here. Toon Link (conceptually, at least) can do everything Young Link can do, but better. There would be no point in him. He's also the only character in smash history to be replaced by someone. And frankly, his replacement is a lot more popular, important, etc. Again, no point in him anymore...
Pichu: The only character in Smash Brothers history to be downright thrown out. Although I see him as more likely than Young Link, I think it's safe to say that we will never see him again. However, if we get DLC, I think he's a prime candidate.
Bowser Jr.: My preferred choice for a Mario newcomer, but I personally have doubts about him. He's important and popular sure, but Toad was that and more... Although I love the little tyke, I don't think we're getting him... He is the most popular of the Mario newcomers though. I think if Sakurai thinks popularity is most important, we'll get him.
Paper Mario: Frankly... I have no idea why people discard the thought of him, so easily. I think he may actually be the most likely Mario newcomer. He's popular, and has stars in an entire sub series. Something no other Mario newcomer can say. While I think it would feel odd to include Jr, over Toad and Waluigi over all of them, I think it would make some lick of sense if Paper Mario got in over Toad. He is Mario after all. I think if Sakurai thinks star power is most important, we'll get Paper Mario.
Waluigi: WAAAA! So... I think he's getting in as an AT again. However, the WAA! is pretty darn popular and doesn't show any sign of going anywhere. However, he has a pretty large hatebase... He's a very divisive character. At least in regards to Smash. I suppose Sakurai could include him if he feels having "the plumbers" is important. For completions sake. Not a likely mindset by any means, but I suppose it's possible.
King K. Rool: Personally, the choices for DK are almost as hard as FE. Both Dixie and King K. Rool have a lot going for them. A lot of the time, people choose one over the other out of preference. Both have a lot of popularity and importance. Both have a lot of star power. Again I think it just comes down to what Sakurai thinks is most important. If Sakurai thinks popularity and uniqueness is most important, I think he'll choose K.Rool.
Dixie Kong: As stated before, I think she and King K have a lot in common. Dixie was planned for Brawl though. If Sakurai wants to revisit his old ideas, then we may very well get Dixie. However, unlike FE, I do think that DK is big enough and that both characters are big enough that we may get two DK newcomers. I don't find it very likely, but it's definitely a possibility. Dixie could also be an easy semiclone if Sakurai is pressed for time, but I think he respects the character too much for that.
Kamek: Oh Kamek! You're so cool! Too bad I doubt you're gonna be in Smash 4. However... I think it's entirely possible for Kamek to be in the next one. He's getting a LOT of roles recently. Nintendo is finally remembering him and it makes me happy. Hopefully, in Smash 5, he can be seen as a real contender!
Toon Zelda / Toon Sheik / Tetra: A character with a lot on controversy... She was planned for Brawl. Which says a lot actually. Sakurai actually considered her and possibly considered making a completely original character in Toon Sheik. Honestly, I'm not sure what to say about her, other than she has a chance. I dunno. She could be an easy character to develop if pressed for time, but I'm not sure Sakurai will be in that situation.
Tingle: KOOLIMPAH! This is an interesting character. Do not steal him. Tingle, like Waluigi, has a hatebase, and a BIG one at that. However, unlike Waluigi, Tingle is a very important character in the Zelda series. And has even starred in his own series. His inclusion would turn a few heads but at the same time is pretty logical considering his importance...
Ridley: Ridley is an interesting characters. One of the most important and popular characters left. He has a large amount of star power, especially compared to his competition. The only characters that can compare to his star power are Pac-Man, Mewtwo, K.Rool, Dixe, Mario characters and arguably Little Mac. He's got a lot going for him, so why isn't he considered a shoo-in? Possibly because he's one of the most controversial characters yet. Is he too big? Is he a stage hazard? Is he a boss again? Is he finally playable? Frankly, it's a crap shoot. He could be anything. The only thing we can really do at this point is wait and see.
Bandana Dee: The most likely Kirby newcomer. By far. He's popular, important and downright adorable. However, the demand for a Kirby newcomer is pretty low. Many people view the series as complete with Kirby, Meta Knight, and King Dedede. I don't think we'll see him this time around. However, he's one of those characters that could be a good choice for the next game.
Krystal: Another divisive character. She's a lot like Bandana Dee actually. Popular and important she's a pretty wanted character. However, she has the same problem Bandana Dee has. Many people view Starfox as complete and most don't want Falco or Wolf to leave and I doubt Sakurai will cut either of them. I think she'll sit this one out personally. Maybe, if Starfox gets more games and she stays important we could see her in Smash 5.
Palutena: The only likely choice for a Kid Icarus newcomer. No Medusa. No Magnus (WHY DO PEOPLE KEEP INSISTING HE'S A SHOO-IN!?!?!). She's popular around the world, important and has little to no competition or problems with her inclusion. I think she has a pretty likely chance of being included. Some people say Sakurai's humbleness will keep her out, but I doubt it.
Chrom:Oh... boy.... Chrom. Well, I think he's about as likely as Roy. He's popular (though not as much Roy), important and is marketed a lot. He and Lucina are even getting skins in Monster Hunter. DO YOU REALIZE HOW HUGE THAT IS?!?! It's the equviliant of GTA over in Japan. Frankly, I think that Sakurai will choose Chrom if he thinks marketability and recency (it plays a part, don't say it means nothing) are most important.
My Unit / Avatar / Robin: A bit of a surprise choice. There's not much reason to add Robin over Roy or Chrom sadly. However, I do think that Sakurai might add him if he finds uniqueness important.
Little Mac: Practically confirmed. That boxing ring man. It's obviously Punch Out!! inspired. Combine that with the facts that he's incredibly popular and important and you got yourself the only character we can call a shoo-in.
Isaac: A character I'm not sure where his chances lie... He's pretty popular in the west and Golden Sun has quite the legacy... but Sakurai could easily overlook his series. I'm just gonna go and say 50-50.
Shulk: Like Isaac, I'm not sure... He's got a chance yeah.... I think I'm gonna say 50-50 for him too. His case is pretty similar to Isaac.
Takamaru: If we're getting a retro character. It's him. He's the most popular retro choice and probably has the most star power out of all reasonable retro choices. However, I am starting to doubt a retro character in general. I think a condensed roster may really hinder his chances.
Mii: I think they're incredibly likely. They show up in everything. They're popular (not here, but almost everywhere else) and important being a part of one of Nintendo's main series now. Their implementation may cause problems, but Sakurai will definitely consider them.
Pac-Man: The only new 3rd party character we're gonna get. He's the only real legendary character left. Namco helping may get him noticed but ultimately its up to whether Sakurai thinks he's worth it.
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My thoughts on things. Please tell me what you think. I can elaborate as well, if you wish.
EDIT: I really would like to hear your thoughts guys. I don't want just likes...