I tend to be optimistic, that's just me
About the stages, it's seems normal that it get a stage on both versions. We just know it, while we are waiting for other stages (I still want to know what the F-Zero stage will be, for exemple)
About the assist trophies, let's compare with Zelda and Metroid. Zelda have it's main characters playable (Link, Zelda, Ganondorf, plus Sheik and Toon Link as "bonuses") and the assist trophies are secondary, but popular characters.
In Metroid case, as there's not a lot a main characters suitable for being playable, the assist trophies we get are really big names of the serie: Mother Brain and Dark Samus, basically the main villains. There's also the serie's "mascot", the Metroid. We also know that Ridley's here, even if we don't know his role yet.
Back to Kid Icarus, we can see that the representation is more like Zelda.
With SSB4, I see Sakurai's opportunity to throw as many Kid Icarus content as possible. We don't know when will be the next game, after all. It's a bit like Kirby: we got Dedede and Metaknight at the same time.
And Medusa is last main character missing, with Hades. Medusa have a lot to bring to the crossover aspect: she is a female villain, and a classic character. It can be interesting to fight Palutena and Pit as Medusa, as much as it could be fun to team up her with Ganondorf (classic 1986 who were ugly beasts before becoming sexy villains
). Finally, we can all agree that she can be a unique fighter.