Put me down as a supporter. While Palutena seems almost guaranteed at this point (though there's always the possibility that everybody turns out to be catastrophically wrong about that, but it's a rather slim chance), and I'm very excited to see how she turns out, Medusa is no small contender for a third KI character, as this thread has argued fairly well; indeed, I would wager she's the most likely candidate for that spot. I see no reason why she would end up being a clone that isn't "time constraints" (ala Ganondorf, who made it in primarily because he had a similar body type to C. Falcon and that meant they had a way to just barely squeeze him in there) or "we were lazy, okay," which I highly doubt would be an actually admitted reason. I don't really see Medusa getting in before Palutena, but easily alongside.
She has enough to draw from to put together an interesting moveset, whatever that may be, she has importance over the vast majority of the characters introduced in Uprising, and seniority over all of them. Her mere presence wouldn't be spoileriffic for Uprising, which Hades, the main other major contender for the third slot (in my view, anyway), distinctly would be, his reveal in Uprising being the point where the game lets you know "hey, you know the simple plot you've had so far? About that..." (it didn't stop Lucas from bringing in all kinds of horrible spoilers for Mother 3 with his inclusion in Brawl, but that wasn't an inherent problem with Lucas, just a problem with how they decided to represent stuff like trophies and Porky; I would also wager Uprising being a creation of Sakurai's would make him more mindful of including spoilers, but admittedly he's done stranger things, so who knows).
She's female and a villain, two points in her favor in terms of representation (assuming either or both are concerns of the development team; there's evidence to indicate they're aiming to include more female characters, but little to indicate that villain inclusion is given even vaguely similar priority); indeed, Palutena and Medusa being the two newcomers for Kid Icarus would probably be greatly appreciated by a fairly large crowd for making one franchise repped dominantly by female characters (Uprising's goddesses did much to drive the plot, after all), far bigger than any crowd that would actively detest that same fact (though perhaps less than the crowd who don't care much either way, but they don't really factor into this point precisely because they wouldn't make any noise either way).
Additionally, while Hades first demonstrates what he can really do in a straight up confrontation two chapters from the end and only fully demonstrates said prowess during the final battle, Medusa has a final boss fight in the original and a major fight in Uprising in which she demonstrates two distinct styles of fighting (and two distinct physical forms taken to use those styles). And personally, she seems more well-suited to Smash Bros. than Hades does, who primarily attacks with barrages of projectile attacks from all over his body and, IIRC, is otherwise reliant on his absolutely gigantic size and god powers, with nothing that really translates to the kind of game that Smash Bros. is. While that hasn't really stopped anyone before, Medusa just seems more at home in Smash than Hades would, with a staff to blast magic from and smack people with, to snakes on her head that can snap at enemies and also potentially fire projectiles, the classic Gorgon stone gaze; perhaps I'm just missing something here, but she just feels like she has more going for her.
And perhaps above all for personal reasons for wanting her in the game? A stone gaze special move just sounds like it would be the most delightfully mean thing to spam; even if it's properly balanced for actual fighting, spamming a move that temporarily petrifies people each time it hits is sure to create many entertaining moments. In general, Medusa strikes me as being a fighter focused on screwing your opponents over with unusual status effects, keeping yourself fine and dandy while your enemies try to break through your strange defenses, but perhaps faltering in terms of killing power when it comes time to send them flying.
TL;DR: Medusa seems cool and more likely than some might think.