I DO hope we get some out-of-left-field forgotten character in Smash, I love what Sakurai has done with Pit and the Ice Climbers. Every new character in Smash has had at least one new game since Brawl, and while this is no surprise considering Sakurai has, in the past, lamented the lack of newer franchises he could incorporate, it's a little sad because I love seeing old characters get makeovers for Smash.
There haven't been any forgotten characters in SSB4 (well, maybe Megaman), but I'd say Wii Fit Trainer and Chorus Men will fill the surprise role well.