Since Sakurai seems to enjoy throwing in references to other Nintendo games, I wonder if we'll get some cameo weapons. Samus's arm cannon seems obvious, Mario's glove could shoot fireballs, the Master Sword, Dedede's hammer. Could be fun.
We've already seen some cameo appearances: There are Nintendogs-themed orbitars (two dog paws hovering by Pit's shoulders that cause pawprints to appear onscreen), and an actual Metroid is one of the enemies in the game. Both of these cameos have already been seen in screenshots.
Not to get sidetracked, but maybe with Sakurai's level of involvement with Kid Icarus, the franchise will get more love in the next Smash Bros. It'd be nice to see more than just Pit; I'd love to see a playable Eggplant Wizard and an extra stage or two.
Definitely expect more Kid Icarus characters in Smash Bros. on 3DS and WiiU.
In fact, I wouldn't be surprised if they changed Pit's Final Smash to be the three Sacred Treasures of Light; in one of the trailers for Uprising, we see Pit donning the items to become a golden centurion version of himself, which then does battle with Medusa. Consider it his "Super Saiyan" form. I could easily see this becoming a new Final Smash for him, freeing up Palutena to be her own character, preferably alongside Medusa. Speaking of which, Medusa would be a fantastic character: finally, an evil (and non-blonde!) female character, with no shortage of magic and minions to compose her specials. And her physical attacks could make use of her scepter. It's too perfect, really.
Another Uprising character, Magnus, "the strongest human on Earth," almost seems like he was designed with Smash Bros. in mind. He fights at your side at certain points in Uprising, and was designed as a foil to Pit, strong and masculine with a massive broadsword as his weapon. He would fit a game like Smash Bros. perfectly, as well.
Sakurai clearly went all-out retooling the designs of every existing Kid Icarus character and adding boatloads of new ones. With Uprising, Sakurai has single-handedly created more "new" and "renewed" characters than any other Nintendo game in recent memory. It's like he knows Nintendo has been slacking with characters that could fill out a Smash Bros. roster, so he's making them up himself.