This is based on Roman Reigns staying Champion until past WrestleMania. If this happens, here are some of his potential WrestleMania opponents after the Royal Rumble match:
1) Triple H
They have been feuding for the past little while and it is clear that something is brewing. Reigns took out Triple H at TLC and sent him to the hospital. They have clearly been hinting at a future Triple H vs Roman Reigns match. A suggestion I have heard thrown around is that Triple H puts himself into the Royal Rumble at #30 and wins it, setting up him vs Reigns for the WWE title at WrestleMania.
The problem with this scenario is that I hate Triple H getting a title shot in 2016 when he wrestles once or twice a year. I think they need to make new stars and not rely on older guys all the time. Triple H winning would bring a lot of heat though so it is a possibility.
2) Brock Lesnar
We saw this match at last years WrestleMania but a lot of people are saying it could happen again. If Brock Lesnar enters the Royal Rumble, he instantly becomes the HEAVY favourite. Hard to see Brock Lesnar getting eliminated by anyone on the roster and have it make sense. Just because of who he is, Lesnar is a candidate to face Reigns for the title.
3) John Cena
This is another situation that could easily happen. John Cena wins the Rumble and faces Reigns for the title. The WWE might want to allow John Cena to win his 16th World Title on the biggest stage of them all in 2016. John Cena is always a threat to win the Royal Rumble.
4) Kevin Owens
This one is a bit of a stretch but Kevin Owens could win the rumble and face Reigns at WM. Owens is arguably the top heel in the WWE right now with Seth going down with an injury and could align himself with the Authority in order to get a high Rumble spot.
Other options: Sheamus? Ambrose? Wyatt??
Let us know what you think and if I missed anyone! Let us know what scenario makes sense to you!