Goldberg, lesnar, reigns, rollins, cena, Owens, styles, joe, Nakamura.
^ me almost a month ago, and I still think all have good reasons and "Vince reasons" to win, I'll struggle to name 5.
I also omitted Balor previously, like a moron. Y2J is gone after Mania and just doesn't wrestle like a rumble winner, unless he does the complete sneaky chickenshit he has done before and, as others have said, they don't need a Rumble win to set up Jerico vs Owens...
...but they do if they want Owens to hold onto the Universal title... actually I've convinced myself it's possible while writing this.
Goldberg: Who's going to eliminate him? Kayfabe the strongest wrestler ever in history, squashed the man who overcame Taker magic at Mania, bitched out Cena, beat Cena and Rollins simultaneously, undisputed champion for months.... also having Lesnar win the Universal title when he returns, maybe in EC (or is that an SD ppv?) is a great way to rebuild his dominance, and sets Goldberg-Lesnar III at Mania for the title, which we haven't seen from their matches. Vince reason is that he would want Goldberg-Lesnar III to main event, because casuals.
Lesnar: Inverse of above: starts his rebuild by eliminating Goldberg then wins the thing, immediately he's a big deal again. Less likely because it means Goldberg has to win the belt to set up the match, which I don't see happening.
Also, possible that we get hit with the swerve and both Lesnar and Goldberg put over other people at Mania (what I'd do, Lesnar ever beating Goldberg is unbelievable now), in which case one of them losing a Universal title match to put over Owens as a strong champion to undo what's gone before with him needing help from Jericho (believable because 265lbs and can do a swanton, flight advantage and isn't getting totally rekt for strength), or going to SD to face AJ and cement him as the greatest technical wrestler and high flyer of all time, by running rings around Brock or Goldberg. He needs it less but that'd be fantastic. So yeah, two ways that either Bill or Brock can win the thing.
Reigns: Because Vince still believes him in as a babyface and adores his oily Samoan muscles like they're children of his womb. Seriously though, VKM has tried so hard to make Owens hatable so Roman can go against him as the face, and he put him against Rusev to try and take advantage of the fact that anyone (except apparently Roman) will be cheered against Rusev if they focus on disparaging the USA. It's not working, but Vince may well still try. Roman wins a third Rumble and he becomes Austin, and, well,
he got over, so
Roman will too, right?!?!?!?!?! If making him The Rock won't work, we'll make him Stone Cold!!!
oh my god they already did stuff with beer oh god this is actually the plan fml
Only catch is that Roman just faced Owens for the title. If they're still doing the thing where you get to choose who you face (i.e. Rumble win also lets you trade if you want) he might opt for Styles, but then they did that already too. But the part of me that believes Vince cannot escape the 60s and is an utter deluded madman thinks he might actually have Reigns win again.
Rollins: One option that I don't stand by. It's very clear that his thing is to run through Jericho to get to Owens, and to go through KO to draw out Triple H, who betrayed him for Owens. If he's getting to Triple H in time for Mania, he has to get to the title (probably have HHH cost him it again) before then, so no Rumble win.
Cena: As in OP. It's the way other than Lesnar and Goldberg for the belt that Vince puts on a casual-friendly ME, Cena-Styles for the belt could very well be an all time great Mania ME too. But as far as I'm concerned he's the only match for Undertaker left that would matter, so I think this is way less likely than the bookies and everyone else seem to believe. If Cena wins the Rumble what on Earth can Taker do?!
Owens: N/A because champion, but was very possible if he lost the belt due to Jericho at any point and again, would've strengthened him.
Styles: ^
Samoa Joe: Nothing left to do in NXT, and a perfect fit for the main roster right now. If he didn't come up after he first lost the title then this is the time that's left, really. Would be an all time great shock Rumble win, yet totally believable. Could make a main event star for decades to come.
Nakamura: See above. Either of these works in either the role of Rumble winner/top eliminator or NXT Champion, but I think Joe in the Rumble and Naka with the belt works because it means both positions have someone fresher. Naka also isn't that well oriented to the Rumble with strike offence, but if you want to build crazy Japanese man as a threat, this is a way to do it. But he's NXT champion so while he might enter he's unlikely to win.
Balor: Because obviously, epic Rumble return and reminds everyone that he's fucking great. Although, it's what everyone expects and he's entitled to a 1v1 title shot regardless because he never lost the belt.
So to my mind, the 5 people that can win the Rumble are, in no particular order:
Balor
Joe/Nakamura (whichever isn't NXT Champion in six weeks' time xD)
Reigns
Lesnar
Goldberg
Looking forward to this, least predictable rumble in years.