We don't really know what to expect from Ninja Gaiden III, especially since Itagaki has left Tecmo and the series behind (in some juicy, juicy gaming drama). The new designer Yosuke Hayashi has many times said that we should expect a darker ninja-game, where will see a new side of protagonist Ryu Hayabusa (all while he chops off the limbs of demons, presumably).
In an interview with Playstation: The Official Magazine, Hayashi has now said that Ninja Gaiden III will come with multiplayer, even going as far as saying that it will include "complex" multiplayer features. What complex means in this context is anybody's guess, but we assume it has something to do with chopping off limbs. Probably from giant demons.