Hacksaw Jim Duggan will more than likely be making an appearance, given that it's the 30th anniversary of the Rumble.
Expect other past winners to join in as well.
...Then again, looking at other winners is a little sad, considering the "Where are they now?" factor:
Big John Studd (Dead)
Hogan (I mean, that'd be a great way to bring him back for one night)
Ric Flair (doubtful)
Yokozuna (Dead)
Bret (Retired)/Luger (Retired)
HBK (Retired)
Stone Cold (Retired)
Vince McMahon (Yea... no. Also injured)
HHH (Expected)
Brock (Already announced)
Benoit (Dead)
Batista (Would be a nice tip for his upcoming Guardians of the Galaxy 2 release... Has a movie releasing this weekend, too)
Rey Mysterio (Probably not)
Undertaker (Already announced)
John Cena (facing AJ for WWE title. Still possibility)
Randy Orton (Already announced)
Edge (Retired)
ADR (Ha. Ha. Ha.)
Sheamus (Already announced)
Roman Reigns (Already announced)
Very few options, here. Basically Hacksaw and Batista would be the best surprises from past winners. Hogan would be an interesting surprise, too.