The question is whether Marth, Toon Link, and Lucario (to a lesser extent, Luigi as well, though Sakurai's own comment in his reveal PotD suggests he is still unlockable and was revealed only because of it being the Year of Luigi) are still unlockables - meaning Sakurai is probably gonna reveal the entire roster; newcomers, unlockable or otherwise, are going to all be revealed regardless, if I judge Sakurai's comments correctly - or if they're starters. If they're starters, then who's waiting just behind the shrouded mist of unlockability? Ike? Pokemon Trainer? Ganondorf? Or maybe.... *BAM* GENESECT, ROBIN, VAATI!
*ahem* Yeah, haha. But with the release date confirmed officialy on-track for 2014, and rumors suggesting it to be sometime this Spring or in the Summer, regardless of which of the three is true we're going to get to the point where Sakurai is gonna go all out on revealing the heavy-hitting stuff in droves as we get closer to release. Not everything, but he's probably gonna hit us with characters like Ridley, K. Rool, Little Mac, Takamaru, Mewtwo, perhaps Palutena, Shulk, and Black Shadow(?) as well - the most-wanted characters between the West and Japan - as the date of release draws nearer. Once it's the next game on the horizon, Nintendo's gonna go full-on with marketing it - we'll probably get a Direct dedicated to it, where we'll see a few new newcomers/veterans.
As far as predicting reveals, however, Diddy Kong is still the latest and greatest bet; after him, it could be anybody in a Direct that we're almost guaranteed to have this month due to the lack of one in January,