Well, as I stated, we reached the numbers of Brawl's new franchises, 6. I have no doubts we will get more (where are you, Advance Wars?!), but, as someone who wants new franchises, I do admit that we also need to represent the existing series correctly. Considering Kid Icarus is one of Smash Bros main franchise now, that we have "less important characters" as assist trophies and that Medusa is a classic villain who have absolutely no mentions so far, it's fair to think she have a good shot to be playable (not a shoe in, though). She was in Captain N after all!
Also, with Villager, and to an extent Wii Fit Trainer (but just because of the sales) and the Miis, I think we have the missing "big names", since Brawl. For example, I see Punch Out as a good ol' classic, but also as a less important serie.
About the leak, I still think there's part of truth (basically, half of the first leak) and part of fake (basically the rest). If he knew about Little Mac, Pac-Man and Miis, I wonder why he wouldn't know about Rosalina. And I think that except the characters shown at E3 2013, the other ones were easy guesses. Time will tell (and it's not really the place to discuss about the leak legitimacy)