Honestly I would take any of the Kid Icarus characters as new Smash Bros. characters. What will likely end up happening though is many will become Assist Trophies. Realistically the only new ones that are going to be added as full characters (other than Pit of course) will be Palutena and/or Hades simply due to their plot significance, continued appearance for most of the game, and demonstrated fighting abilities. Everyone else, while cool, only shows up briefly for a chapter or two and thus aren't really viable candidates. The only other characters to show up with some frequency are Viridi and Medusa and honestly that first one displays no battle prowess in the game. Both of those also have the disadvantage of fulfilling similar roles to Palutena and Hades...who like I said I think are both more likely.
Finished the campaign this afternoon. Loved it to pieces -- wildly charming story and writing, exhilaratingly paced gameplay, endless customization -- I can't praise it enough. When a game can strip away my desire to look at it from a design/critical perspective and instead make me look on in child-eyed wonder (not to mention change my NeoGAF avatar, of all things), I know it's completely won me over. I had no idea this would become one of my favorite Nintendo games in the span of what, three days? So good. I very much look forward to future explorations of the KI-verse, as well as the next Smash Brothers installments!
Speaking of which, the whole time I was playing I was thinking about who from Uprising should be in the next Smash Brothers! In terms of character design, personality and fighting style I really liked Arlon and Phosphora, even though their roles in the story were both woefully small. Unfortunately, a lot of the characters aside from say, Palutena (who I wouldn't mind) -- as cool as they may have been -- were lacking in either relevance to the story (i.e. the aforementioned two) or displayed battle prowess (i.e. Viridi). And while the Smash team can compensate for the latter, the former is most definitely an obstacle.
I don't think she realized that at the beginning. If I remember right i thought she was confused about it or didn't think she was...or something to that effect. I need to replay Chapter 9 to be sure but I am fairly certain there is dialogue about it in there.
Spoilers for final chapter:
Does anyone know why Medusa helps Pit and betrays Hades, exactly? I know she was tired of being a puppet, but she didn't seem to mind all that much at the beginning of the game.
Did she just not want Hades consuming all of existence or something? :P