Ridley would be such a megaton in the Smash Bros. community that I suspect they'd save him for E3.
Bayonetta would cause similar meltdowns, albeit you'd have the tweenager fans that want Shadow the Hedgehog raising a ruckus.
Satisfying but safely predictable reveals are Palutena, Mii and Pac-Man. The leaks/rumors to their inclusion are yet to be debunked. And there are clues like the Find Mii stage, Palutena's Temple, etc.
The Monolith Soft person tweeting this Direct makes a few scenarios seem possible: 1) Monolith likes helping a brother out; 2) Smash Direct won't be just Smash news, but also include mentions of other upcoming games, like X; and/or 3) playable Monolith character in Smash, perhaps Shulk -- this would feel right given Sakurai posting pics of the sword at the concert, and a Nomura-esque-looking character with a red sword and clairvoyant powers would certainly feel unique even with a couple other blonde-ish swordsmen on the roster.
Of course, there is the question of a Fire Emblem rep, with the latest installment, Awakening, having no shortage of wonderful characters and character combinations to choose from. I'm still rooting for a Pair Up character in the form of Chrom & Lucina.
A super-satisfying veterans reveal would be some combination of characters including Snake (now more likely to be back after the Raiden voice actor mentioning his character's involvement in Smash, although it might've been a miscommunication; personally, I've always believed he will return). Ideally, they'd show veterans that people feel uncertain about for whatever reason... Ice Climbers, R.O.B. and Wolf would be nice.
So many exciting possibilities! ...as well as the not-so-exciting possibility that they won't show any new characters, lol.