Fire Emblem and Mother are 1st Party franchises. However, Kirby is a 2nd party franchise as well as Pokémon (since HAL makes the Kirby games and it's a 2nd party developer). Kirby got in since Sakurai created the franchise, and Pokémon since it is only one of the biggest phenomenon's in gaming history.
Actually, for this very reason, I find 2nd party franchises that are not made by HAL or are extremely popular to be highly unlikely in general. This is why I am not a fervent supporter of Isaac since his chances were never that great to begin with being 2nd party and all.
But assuming that we have 12 more returning veterans (including Mewtwo), and a cast of 60 playable characters, who does everybody think is very likely to make it in and why? Me, personally, 8-Bit Mario, King K. Rool, Dixie Kong, Chorus Kids, Ghirahim, Ridley, Dark Pit, Takamaru, Bandana Dee, and Shulk are the only characters I can think of in which hints may have been planted for, but that's shy the two characters needed to fill the 60-characer roster. All of them have obvious (or likely, albeit straw-grasping) pieces of evidence for and/or against their possible inclusions that have been stated time and time again (although with Takamaru's game coming out internationally on VC for the first time ever at this point and time does help his chances quite a bit, methinks).