I think the Yoshi series needs a 2nd representant. Yoshi's Island DS sold very well and is the last real Yoshi game I can think of. Two Yoshi games are on the go, so yeah: I believe Yoshi will finally get a 2nd representant. The really strong franchises have already more representants and even a weak franchise like Star Fox has 3 characters. (only 6 games without remakes, meaning less games than F-Zero) For SSB4 like for other series in Brawl already, there is a need to give some One Representant franchises more spots. I can think of four One Representant franchises that could offer another character for SSB4: Yoshi series, Wario Land/WarioWare series, Kid Icarus series and the F-Zero series. However F-Zero seems to have no other really representative character apart from Captain Falcon. Is Black Shadow good for promoting SSB4? Not really. Samurai Goroh? Neither. Judy Foster? I guess no. And the way around: Could SSB4 by implementing Black Shadow, Samurai Goroh or Judy Foster push the F-Zero series? Well to push a quite inactive franchise like F-Zero, you first need new games you can push. As there seem no new F-Zero titles to come in the future, there is no need for more F-Zero characters.
Kid Icarus will get a 2nd representant to show it's not the death franchise as we knew it in Brawl. (Sakurai surely wants to push Kid Icarus:Uprising)
Anyway, to come back to the topic. As we only have three franchises that could get a 2nd representant, I'm pretty sure 2 out of 3 if not all 3 will get more representants. Look at Brawl: Kirby and Donkey Kong, Metroid and even Earthbound/Mother got a 2nd representant. (Kirby even got a 3rd one) I feel like a 2nd Yoshi representant is out of question, we will get a 2nd one and I'm supporting Kamek.