Guess I'll go and revive this.
After listening to the music of SW4 on youtube and reading up some details on the game, I'm actually kind of enthusiastic for the game's release in the West.
As I understand it, SW4's focus is on bonds between certain characters. For that reason, it seems like you play 2 characters and switch between them in the game's stages. They've added a bunch of characters to fill out the factions in order to accommodate this gameplay change. For example, they added Koshosho who is some wife or concubine of Chosokabe Motochika. They added Shimazu Toyohisa for the Shimazu and Kenshin's eventual heir, Uesugi Kagekatsu, to the Uesugi. They also added Sanada Nobuyuki, Yukimura's brother who sided with Ieyasu and was married to Tadakatsu's daughter. Most of the new characters seem to be calculated additions who you play in tandem with somebody else. For example, in the early Takeda stages you can pair Sanada Nobuyuki with Sanada Yukimura or Sanada Yukimura with "Kunoichi." If you play as the Tachibana, you'll play the duo of Tachibana Ginchiyo and Tachibana Muneshige.
Cao Hong 14 got his wish with Katsuyori, sort of. Takeda Katsuyori and Uesugi Kagetora appear to be special NPCs in the game along with Saito Dosan and Sue Harukata. They're actually playable, albeit with somewhat generic weapons, in one of the game's modes. All of these are interesting choices and I wouldn't be surprised to see them become playable in an SW4 expansion.
I have to say that I'm impressed with how SW's roster is coming along. It started out so small but they've really filled out the factions. The Azai, Takeda and Uesugi, which before had barely any representation, are now pretty large. Along the way, Koei has even added some new factions like the Mouri and Houjo.