Eh.. last time I checked Snake was a God-tier videogame character in terms of popularity in Japan. Bayonetta doesn't really come close to that.
I don't have anything against Bayonetta, and I'm as neutral on her as I'm about Snake. But something just feels really off to me about supporting her.
Her concept IS being oversexualized. Her means of attack, from what I understand, leave her almost naked. And her other means of attack are guns, something that Sakurai is against for this game. (Unless they're laser guns, that is)
But as far as 3rd party characters go, I don't see SSB gaining anything from her inclusion. (Especially with just two games under her belt (3 if you count Anarchy Reigns), and only one of them for Nintendo systems).
Still.... would be cool to see her I guess.