The only things I see worth noting are, Pit, Palutena, and Medusa are the three characters from uprising who actually represent the series. Everyone else from Uprising is a one-game character who were made by Sakurai for Uprising. And Sakurai doesn't particularly seem to like fluffing the roster with his own characters. Which is frine. But then we've got Palutena and Medusa.
+ Palutena is the more popular character.
+ Palutena was in the one US-exclusive Kid Icarus game, who knows how much Sakurai even cares about that though.
- Palutena as a sort of "princess", "goddess", and "light-based magic user" is kind of redundant conceptually when we have Zelda and Rosalina. That IN AND OF ITSELF is not a problem, but when you put it together with everything else, it adds up pretty heavily.
- Palutena has a role in the series as Pit's final smash. As much as I don't like using this evidence as a Ridley supporter, Ridley has had different roles throughout the smash series and Palutena hasn't. You can disregard that if you will. But it's something to note.
- Palutena isn't the best option for a crossover fighter of this nature, which I'll elaborate on in a moment.
- Medusa isn't as popular of a choice. She also wasn't in the second Kid Icarus game starring Pit, Palutena, and... Orcos. Yep. BUT...
+ She would be a more "surprising" reveal. Sakurai seems to like characters who are valid for their purpose on the roster, but are still surprising to build hype or interest in the game.
+ Medusa IS, Myths and Monsters or not, the classic 1980's antagonist of the Kid Icarus series. And even if she gets moved to being the first arc boss of Uprising, her status isn't removed. If it worked that way, Ganondorf would be cut for sure after being shafted by Malladus, Bellum, Yuga, and Demise in the last several zelda games.
+ Medusa would be, of course, our first dark magic character and female villain on the roster. Ganondorf just kind of punches things. That isn't magic. And being based off of Medusa (Wow really) and considering how she is in combat, she is capable of an in-character bizarre stunning and trapping game with bizarre projectiles to force opponents to be where she wants them to rack up damage and compensate for weaker melee attacks.
+ It basically comes down to a choice. Sakurai can work harder to make Palutena unique from the other characters who edge into the same niche as her on the roster AND make a new final smash for Pit on top of the one for Palutena. Or, he could provide a surprising major character as a close alternative who would take less effort to make unique from the rest of the roster.
I mean, I'm not Sakurai. But if I were and I had the choice between two major characters, I would pick the one people would be surprised to see and make them so good that people are happy to play them... instead of picking the character people expected and are happy to see, but isn't as different or interesting as they could be.
And what I meant on the subject of options for a crossover. When it comes down to it, fights like Mario vs Peach, Link vs Zelda, and Pit vs Palutena aren't the kinds of grudge matches people want from a crossover. People want to see Bowser finally beat Mario by teaming up with Ganondorf, or maybe Wolf and Wario beating the tar out of each other. Villains are good for this sort of thing and are a good contribution to a crossover environment. Especially if they're a classic and mean a lot to an older series.
TL;DR, I feel like Medusa is competing a lot more with Palutena than people think. A lot closer. It could go either way, but I think we'll definitely see one of the two at the very least. Or maybe we'll just get all three. That'd be pretty amazing too.