WWE is interested in bringing back several former mid-card wrestlers to fill out the roster, help the company's younger talent get over and improve live event attendance, particularly the SmackDown brand.
Some of the names discussed include John Morrison, Shelton Benjamin, MVP and Low Ki (formerly Kaval in NXT). Shetlon Benjamin recently got out of his Ring of Honor contract and is seen as one of the wrestlers most likely to be returning. MVP recently stated on Twitter that he's open to returning, but he is currently under contract to New Japan pro wrestling and is very satisfied working overseas.
Aside from these names, other superstars discussed for possible Royal Rumble returns include Tommy Dreamer and the New Age Outlaws. There's also a possibility we'll see Christian return at the Rumble, since he's ready to return to action this month after a several month absence.
(Partial source: PWInsider)