It'll be a pretty big deal for Ryback (and The Shield) if they main event. When was the last time a PPV main event didn't include Cena (but he was still on the card?)
No Punk/WWE title means it's all on them as the main attraction
“I want people to dream about their football club. They should, we should all be dreamers at heart. Some people are the opposite and say ‘we can’t do that’, but when you ask them why, they can’t give a reason. Well, I say, ‘Why not?’” - Kevin Keegan
If Ziggler's going to cash in and win the world title so that his match with Cena will be for the world title then Cena/Ziggler will. Otherwise I don't know, probably the 6 man pinfall/submission TLC tag.