Well, if you really want to find some way for you to be RIGHT.
I wonder how many other characters are like the Villager. Sakurai has said he had a lot of other ideas for characters, and I bet he wasn't just referring to the Forbidden 7.
Sakurai could also have considered quite some characters who are Assist Throphies to be playable. Most noticably Saki, Isaac, Jill, Lyn and perhaps even Waluigi, and Knuckle Joe. From them all, I can only right now consider the first 2 to be viable choices, but that doesn't mean the others cannot be brought up as well. Maybe Shadow and the Metal Gear swords guy where considered as well?
It's overall enthausiasm of the team to actually WANT TO MAKE THAT CHARACTER, which could come out of overall popularity (as in: will this please the fans more than X character?) or overall ability to make them fit in and be unique and they could've come with with troubles for Isaac, Saki and Jill in the fitting in regard.
And I guess we have a new team working on Smash 4 wasn't that right? Sakurai himself stated somewhere he doesn't quite know who the team is, and that Nintendo picked some guys for him to work with. That could either end up as good, as in experienced staff members will be able to get the characters to fit in better with previous expeirences, or bad: a new team will probably only add in characters that fit in easily enough and characters very populary demanded. Therefore I wouldn't count on Ridley or K.Rool as much yet, as those characters would take quite some expeirenced staff members.
Coming back to Zelda again, I think that if Impa is as much as even suggested she'll get worked on for sure, cause the team would regonsize that with Sheik it's possible for Impa to fit in just as easily. Remember that some movesets don't write their own, and they had to come up for a lot of stuff for characters as Fox, Captain Falcon, Zero Suit Samus and Sheik who all have totally made up B moves except for a few (ZSS's B for example). Impa has more stuff to work with than most other recent Zelda characters, with the sole exeption being Ghirahim. Who might be in the Midna category of extremely popular and fitting, but not making it probably due to being a one off.
Note that Skyward Sword especially was hyped up by Nintendo a lot, with tons of trailers (more than any game I've seen recently) and the stuff about Miyamoto saying that for them it'd be hard to go back to basic botton controlls for Zelda, and that he felt creating a master piece with Skyward Sword. Most likely they remade OoT to have one more "classic" Zelda, though the DS had already games that couldn't even be considered classic anymore, as Phantom Hourglass and Spirit Tracks. Note that SS is also the 25th anniversary game of Zelda, and combined with all this I feel it's far more likely than not we get a characters based on this game. And I say, if Ghirahim has to be that one, it's more likely than not Impa joins in with him. Maybe with a less unique moveset from Sheik than she could've had without Ghirahim, but she'd be in nonetheless.
Also, Skyward Sword outsold Ocaina of Time 3DS.