As far as returning hairstyles, I'd love to see...
-Guys: Unkempt, Styled back (SC3), Medium Hard (SC3), Spiky (SC3), & Martial Artist (SC3)
-Girls: Cassandra's SC4 1p, Updo (Setsuka 2p), Curled Pigtails (Amy), Oriental Frame (Xianghua), Curly Sides (SC3/Abelia), Geisha (SC3), Medium Length (SC3), & Long tied (SC3)
And for hairstyles based off the characters from previous games, I'd love to see
-Guys: Yun Seong (SC2 2p), Kilik (SC2 1p & 2p), Mitsurugi (All of his ponytails, especially the one from Soul Blade), Siegfried (SC3 long hair with bangs & his 2p hair), & Raphael (SC2 2p)
-Girls: Taki (SC2 2p & SC1 1p for a longer ponytail), Tira (SC3 1p!), Ivy (SC2 2p), Setsuka (SC3 1p love her Geisha hair), Sophitia (SC3 1p, SC2 2p for nice long hair with parted bangs), Talim (SC2 2p), & Xianghua (SC2 2p)
I also like Garjian's suggestion on the voice. I too would like to see the option of mixing english speakers with japanese speakers. I'd also like them to add in some accent voices. :D