I don't think Tekken, VG, or Soul Calibur are in 3d, persay.
They are generic 3d, as in, they give the illusion of being in 3d, with sidestep and plane changing maneuvers.
However, until you can literally turn your character around and run diagonally away from your opponent, it's not really a full 3D experience.
There was a brawler for Dreamcast, you guys remember that game? It had full 3d and destructable stages. That game was pretty decent, so a decent fighter can be made in full 3d, and it'll be more like Final Fight, Double Dragon, or God Hand, if that's the case.
However, 2d goes with the nature of smash brothers, and changing it would make it a whole different game, which is bad, because we love it how it is.
I don't need your console war.
It feeds the rich while it buries the poor.
You're power hungry, spinnin' stories, and bein' graphics whores.
I don't need your console war.
NO NO, NO NO NO.
