I kind of wonder...is the outfit the only real problem that people have with Mika by now as it pertains to the whole "she's just a sex symbol/fanservice/cheesecake" thing? Unless there's something totally ridiculous that I missed in the trailer, aside from her pro wrestling costume being revealing, her entire personality seems to be based around her combination of positive enthusiasm and raw strength. It seems like they've matured her a bit compared to Alpha 3 in some of her mannerisms too, with her voice having a bit more power behind it, and her hip-drop attack no longer being followed up with her little "look back and rub her ass like it hurt" animation anymore. Instead she's delivering kicks, suplexes, stunners and the like, and all without making those takedowns look particularly cheesy or over-sexual.
It's even funnier to me when compared to Bayonetta, whom people like to bring up as the "she's highly sexualized but she owns it!" standard...when Mika doesn't seem to act anywhere close to that either. She doesn't cap off all of her special moves with poses befitting a centerfold, she doesn't spin around her enemies as though they were stripper poles, she doesn't arch her back and moan while executing attacks...she just kicks people's asses and cheers about it. There's the ass-slap, yes, which as other people have said is both a common taunt of sorts as well as a signal to Nadeshiko to perform their combination attack. Is the double-butt-driver goofy? Yes, but I wouldn't consider it all that "sexy," especially considering the fact that it ends with the victim's face being piledriven into the ground.
If people want to ultimately bitch about the cheesecake outfit anyway, they're free to do so, but again like others have pointed out, the context for it in Mika's case is a hell of a lot stronger already than for Cammy, or, for instance, Chun-Li's black dress alt. She feels so low on the totem pole of fanservice complaints for the time being, at least from what I've seen.