I am down with the Reigns idea...just one thing, do you have Roman(fresh off of defeating HHH) be crushed like Cena(at SummerSlam) was at Survivor Series? I think assuming his in-ring work would still be a WIP, him being crushed also by Brock in first time(Rookie tries to slay the Big Champ) might get people more invested as you suggested for a rematch(assuming hopefully, John Cena will lose again at NoC) and finally be able to slay the Beast Incarnate.
Yeah, I kinda glossed over it because it's a Triple H thread, but that's basically the idea.
Roman Reigns will have beaten Kane on Raw, Randy Orton at SummerSlam, and Seth Rollins at Night of Champions. He comes out the next night asking what Triple H is going to throw at him next. Triple H then decides he has to do this himself, so he beats Roman down and makes the Hell in a Cell match. Roman Reigns beats him clean after a huge brawl of a match, and the next night, Stephanie knows what has to be done. When they couldn't take out Cena, they got Lesnar to do it. So she tells Roman she'll be rewarding him for beating her husband... a WWE title match with Brock Lesnar!
And Roman is pushed like the unstoppable force that can actually take down Brock Lesnar. Hopefully, fans on the internet are even convinced that he's going to be the new Cena and pushed down our throats by hulking up and beating Brock handily.
But at the actual show, Brock will DESTROY him. Roman would have gone in over his head. The people will be in shock over the beat-down Roman received.
After the show, he will be embarrassed, his confidence will be crushed. But he will be sympathetic. Even though he can crush through the competition on Raw, he didn't stand a chance where it meant something. WWE will actually have a powerhouse who's an underdog.
For TLC, Paul Heyman will be part of the build for the 3-way main event, saying that Brock doesn't care who wins. He'll be on commentary for the main event. But when Roman reaches for the contract and it looks like he's going to win, Paul Heyman will flip the ladder and push him down! He'll walk away to the back. That will leave Dean and Seth to fight for the contract, with Dean coming out the winner.
Paul will keep cutting promos on how useless Roman is, adding fuel to the fire for the WM rematch.. But the WM main event will be set in stone when Roman eliminates John Cena last and wins the Royal Rumble. For EC, John challenges Roman to put his title shot on the line in the main event. At the show, Seth Rollins tries to interfere against Roman. But Cena comes out, clocks Seth in the face, comes back in the ring, and turns around into a spear. Roman beats the face of the company, keeps the title shot, and goes onto WrestleMania where he eventually wins the title.
On the other matches:
Agree with Daniel Bryan vs Batista(the build seems sound also)
Agree with Dean Ambrose vs Triple H also(but I'd build it differently.)
I would also do John Cena vs. Seth Rollins after what happened at EC. So WrestleMania would be:
• Roman Reigns vs. Brock Lesnar
• Dean Ambrose vs. Triple H
• John Cena vs. Seth Rollins
• Daniel Bryan vs. Batista
Randy Orton kinda drew the short stick here, since I can't think of who he could face at Mania. There's only so many guys you can push at once. I think putting him into the 31-man Andre Battle Royal would be fine, if they revolve it all around him, and have a new up-and-coming face eliminate Randy last for the win. Although I wouldn't be opposed to Randy actually winning it if they want to build him up as a credible opponent for Roman.