We're still talking about Casual Reps? Did people suddenly become smacked out of their minds over this weekend?? It's not as though Kawashima was suggested for the past few months we've known Wii Fit Trainer would be playable...this is a recent phenomenon.
Wii Fit Trainer hailing from a casual series makes sense, but only when you consider that it's why none of us would have predicted her...few of us are casual gamers, and even if we were to the point of being familiar with her, most would have dismissed her as a dull joke (which...is arguably still the case, but eh). Sakurai has wanted new creations, since he found it strange that none he deemed suitable popped up after Pikmin; he also wants characters that "dance out at him," and he finds it hilarious to stick in shock characters that "pretty much no one guessed would show up." Wii Fit Trainer happened to sit at the point where those three criteria intersect, so he selected her. Just like he had his reasons for adding Snake, yet Snake didn't open the floodgates for any random mature third party character's inclusion, he had his reasons for adding Wii Fit Trainer, yet she doesn't open up the floodgates for any unimportant "casual" NPC's inclusion, let alone multiple ones, regardless of their sales...lest we forget, series don't need characters to be featured in Smash.
Seriously, there's enough damn black-and-white division in the speculation scene with stuff like 'relevance' and 'size,' let's not add more fuel to the bull**** fire with stuff like 'casual' and 'competitive' characters.