I consider Palutena the most likely unannounced character since Pseudo-Palutena in the direct was just way too much of a tease for there not to be something there; you were meant to think it was Palutena and then it was shown not to be, and we also see Palutena no longer appears in Pit's final smash. Sakurai mostly doesn't do subtle hints, but there was really nothing subtle about the Palutena teasing in the direct. Isaac not appearing in the direct could go either way really; it would make sense if he were going to be playable, but he could just as easily have been low priority to show in the direct or even more have been cut as an assist trophy and not appear at all in smash 4. There's no real information we have to distinguish between possibilities.
Either way, this is fairly off-topic. As per the topic at hand, whatever semblance of a pattern Sakurai had for reveals is pretty well out the window, and we're basically in pre-E3 mode at this point. He might feel like showing a veteran or two before E3... or he might want to do another big info dump figuring that will be more overall hype. We don't know when in the summer the 3DS version will come out, but it will be pretty close by E3 so it's likely we'll have seen the entire starting roster by E3 (though not quite guaranteed!). My mindset is that I am expecting a few more important details in the upcoming weeks; in particular, I expect a picture showing us a bit more about how the Pokemon League Wii U stage works sometime soon. However, big new info or any sort of character at all... that's just a bonus at this point. I would be neither surprised nor disappointed if the last two pictures of this week amounted to nothing of consequence.