The rumor going around backstage in WWE is that Roman Reigns is indeed being groomed for an eventual match against Brock Lesnar for the WWE World Heavyweight Championship, most likely at WrestleMania 31.
At this point, Lesnar is pretty much fully expected to get a run with the Title heading into WrestleMania next year. "The Beast" is scheduled to work the upcoming SummerSlam and Night of Champions pay-per-views and WWE officials are reportedly looking to make both of those PPVs as big as possible to help the WWE Network.
No word on when exactly Lesnar might win the Title or who he might win it from, but at this point it would appear as though John Cena will end up dropping the belts to Lesnar which would then lead up to a Brock Lesnar-Roman Reigns feud.
Regarding former World Champion Daniel Bryan, he doesn't seem to be anywhere in the equation in terms of getting back into the Title picture. That could all change depending on when Bryan is medically cleared to wrestle, but as of right now, John Cena, Brock Lesnar, and eventually Roman Reigns are WWE's top priorities for the WWE World Heavyweight Title picture.