This is something I wanted to talk about for a bit.
So with Greninja in Smash, I had said a while back when Rosalina was shown that it seemed they were picking characters who were more recent. I also mentioned in my Roster Analysis that they have always added a new Pokemon character, so that trend looks like it has continued. When you look at the characters in now. They have appered in a recent game. Villager is using a look from City Folk. WFT came into being in 2008 and Rosalina in 2007. Little Mac had a new game in 2010. So with that, here is what I'm thinking will be in the game.
For Sure
Chrom-Fire Emblem Awakening is the best selling Fire Emblem game selling over 1.2 million copies. Based on recent trend, they will likely chose him. He's a popular character so that helps too.
Palutena-Seeing as there is a million things from KI in this game, she would make sense to be in.
Pretty sure-(good chance, but you never know).
Dixie-For those who don't know, Kirby's "Hammer Flip" was planned for Brawl. It seems like Sakurai is bringing stuff that couldn't have been added to Brawl into this game. Dixie Kong was also planned for this game. She has appeared again in Tropical Freeze as well and is a decently popular character
Shulk-Though not as well know, he is very popular (especially in Japan) and his game is highly coveted.
Rhythm Heaven Character-Generally, for new series that have not been in Smash before, the content related to that series is never shown off before the character. In Brawl, Pikmin stuff didn't come out until Olimar was shown. In this game, the stages for Mega Man and WFT weren't shown intil their respective trailers, despite the fact they were within the same day. Rhythm Heaven on the DS sold over 3 million. It will have something in Smash, but nothing has been shown yet. This implies there could be a character.