I'm not reading through this whole thread, so I apologize if this was said earlier. This is how I would book the Rumble if I were in Vince's ear.
This is assuming WWE is adamant about making it Rock-Cena for the title at WM and they want Cena to win the RR (personally, I think it should be those two and Punk in a Triple Threat with Punk getting his WM moment by beating them, but that's not what reports are saying they want, so.....).
I'd have Cena, Ryback, Sheamus, and Orton as the last 4, since they're the ones that have been shown as having the best chance (all 4 are face....it would be odd and memorable) (in the interest of full disclosure, Ziggler would get all the way to 5th left after entering 1st with a great performance by him). After Ziggler is eliminated, those 4 are going at it for another 5-10 minutes. The Shield comes out and the 4 break away from each other. Shield comes in the ring and they each go after one in the ring. Cena sees an opportunity and helps Ambrose eliminate Sheamus, then he helps Rollins eliminate Orton. Ryback throws Reigns and Rollins out before he gets thrown out by Cena and Ambrose. Cena cuts a heel promo talking about how for years, the WWE universe has booed him no matter what he did for them and no matter how many 'bad guys' he tried to beat.
If I (Vince) really wanted to throw some more layers into this, Lesnar would be a surprise entrant at 30 and there would be 5 left in the ring with those 4 plus Lesnar at the time Shield comes out (Ziggler lasting until 6th left). Shield acts like they're there for Lesnar while the 5 wrestlers in the ring act like they have no clue what's going on.....Ryback, Sheamus and Orton still get eliminated, with Cena and Lesnar in the ring left, and then Shield goes after Lesnar and he gets eliminated.
It ties everything together perfectly. Shield going after the other 3 makes sense because that's been their feud for the last month. Shield was Cena's idea 2 months ago when he got injured and he wanted all the Main Event challengers not challenging Punk. WWE presumably shouldn't be wanting an exact replica of Cena-Rock from last year, so turning Cena heel would create a different element to the build up to WM.
Before all the 'Oh no, it's another Cena heel turn guy talking about turning him heel again'....listen, it's gotta happen sometime. If you're going to do it, you might as well do it big and at a time that can be looked at as the change into a new era, which is what it's slowly looking like for the past 2 months. And by doing it like this, you're setting it up so one of the many faces in the WWE can be leveled up and become a true top level star. IWC already complains too much that there's too many faces at the top and not enough good heels.
Also, the Shield has a built in excuse for why they'd help Cena. Simple.....Cena has carried this company for years and has been the biggest star, and yet he gets booed. He's the one moving the most merchandise, he's the one that the WWE goes to every time a 'bad guy' is taking over too much and they need a face.....it's an Injustice that Cena gets treated the way he does, despite every wrestler in the back owing Cena for being the draw that he is and bringing so much money into the company.
Cena doesn't even have to change his attitude all THAT much to pull off a hated heel turn. He can talk about how he sells so much merchandise and always is called upon to win, and he can really play into his 'SuperCena', 'IWC thinks he wins too much' persona. He already played into it a little tonight....he might even be able to incorporate playing to the kids and women in the crowd, while hating on the guys that yell 'Cena sucks'.
I think it could be the start to a new era.....Cena goes on to win at WM....Ryback can be built up to win the title 6 months or so later, as the new superstar face (I'd really like this to be Bryan, since I think he'd be great at it.....WWE should build him up after WM as the Master of Submissions, and he can start getting wins with about 6-8 different big time submissions, and no one ever knows which one is coming....he could finally beat Cena later on in the year)....either way, the next superstar face would be built up in that time.
I really like the idea, and it'd be the way I would do it. Bring on the hate, people.