With a few hours til the next photo, there's various possibilities:
-Another Marth pic since he's the latest character shown to us.
-Another Galaxy pic since it's the latest stage shown to us.
-Zelda revealed, since the release of Mario 3D world for Japan already given us a pic yesterday with the Mario themed pic.
-A Link or TL pic, hopefully something interesting about one of em.
-A similarity to the pic yesterday, but switch the theme from Mario to Zelda. Like to show Link, TL, and a Zelda stage.
Otherwise, it's just another one of his unpredictability moments. So idk which one, but it has to be one of those. The less likely one on my mind not listed there is him giving attention to a character he hasn't shown much of recently, or show off a new item or stage. I just hope it isn't a new Zelda stage as we already have 3 of them. We'll see which one it is.