It could work. I'll admit that I'm not a huge Legend of the Three Caballeros fan due to its oversaturation of supernatural elements. However, if the show is to continue, I think it should work more within the parameters of the "Duckverse." Perhaps a teenaged Huey, Dewey, and Louie (to play off the teenagish April, May, and June) should appear. Maybe Clara Cluck, one of Panchito's love interests, or some members of José's supporting cast in Brazilian comics should appear. Scrooge or Magica could also be a neat addition. Mickey, Pluto, Goofy, Minnie, Max, Roxanne, and Mortimer are all fine characters, but I'm not sure Legend of the Three Caballeros is really the show for them. I feel like Legend of the Three Caballeros is very much a Duck show in the vein of DuckTales, Darkwing Duck, and Quack Pack.
Despite all I just said, I'll repeat again that it could work. It's a neat idea. I just think I, personally, would rather have the show develop both its own world and the greater Duck universe.