In 2002, the WWE kicked off what would become known as the "Brand Extension", where talent was drafted to either the Raw brand or the Smackdown brand, where they would perform exclusively for a year until the next draft.
With the two "brands" essentially being treated as two separate promotions, it made sense for each to have their own set of titles. During the original draft, Brock Lesnar, then WWE "Undisputed" champion, was drafted to the Smackdown brand, leaving Raw without a primary title. Enter Eric Bischoff and Triple H, who decided to dust off the old WCW "Big Gold Belt" and make it the "WWE World Heavyweight Championship".
For the next decade, the WWE Title and World Heavyweight Championship (WHC) were separate. Occasionally, they'd switch brands depending on how the draft fell, but for the most part, they were treated as roughly equal titles in separate "brands."
Come 2012, the idea of the Brand Extension fell by the wayside and two titles were no longer brand exclusive. The WHC quickly fell behind the WWE title in terms of prestige and many fans, including yours truly, felt that the titles should be unified. The logic was simple: there should only be one major title that everyone in the company is aiming for. Having two titles while paying lip service to them being equal when they clearly were not was hurting the prestige of the WHC.
In December of last year, we got our wish. The titles were unified at the TLC pay per view. Randy Orton emerged victorious, now being called "the WWE World Heavyweight Champion."
However, the problems of removing one of the WWE's major title scenes quickly became apparent. Suddenly, there was a slew of near-main-event-level wrestlers left out in the cold. While the Ortons, John Cenas, and Daniel Bryans of the world were able to remain relevant, many were not so lucky. Former contenders for the WHC when it was secondary to the WWE title tumbled down the card. Former champions Alberto Del Rio and Dolph Ziggler have been reduced to the role of "jobbers to the stars" while Damien Sandow, former WHC Money in the Bank holder, has been reduced to jobbing in borderline squash matches. Instead of having a title scene where these upper-mid-carders could battle with descending upper-carders, they've been left out in the cold.
And if you've been paying attention to our daily Rumor Roundup, which I hope you are, you would know that WWE is planning major pushes for Roman Reigns, Bray Wyatt, Big E Langston, and possibly even Antonio Cesaro in the next year. Without a major change, there simply are not enough title scenes to get these guys involved with in order to make their pushes count. (And that doesn't even take into account the fact that WWE would need to find something to do with the Ortons, Cenas, Bryans, and others currently in the main event, as well.)
This is why we should expect to see the WWE and WHC titles split apart before 2014 is over.
According to the various rumors on the subject, WWE officials have kept open the option of splitting the titles, but currently have no plans to actually do so. The reason for this contingency plan is WWE's TV contract negotiations. There are strong rumors that WWE would like to move Smackdown out of the dreaded "Friday Night Death Slot" where ratings are typically much worse than they would be on any other night of the week.
If that means taking Smackdown live on Tuesdays, expect WWE to re-institute something resembling the Brand Extension in order keep both programs fresh. If that is the case, they will once again need two primary titles, which is why they decided to have the WWE World Heavyweight Champion continue to carry both title belts, in order to keep them both in the public eye.
But even if that restructuring of the TV schedule does not come to pass, WWE must strongly consider splitting the titles anyway in order to create more opportunities for the newer talent they wish to push. With separate WWE, WHC, and (a built-up) Intercontinental title scenes, WWE would have three channels in which new talent could be pushed while still allowing room for the usual upper-card contenders to compete. In addition, they can still use non-title storylines to push talent, such as they are rumored to be doing with Bray Wyatt taking on John Cena. While this method can still be effective, I feel that it is less effective than competing for a title, as there is nothing quite like lifting a title belt high in victory for a budding superstar.
As with nearly anything involving WWE, such a drastic course correction would not be something that can occur quickly. I would expect the titles to remain unified through WrestleMania XXX, and likely into the summer. Batista was reportedly promised "a run" with the title in its unified state, and he will probably still get that.
However, by the time SummerSlam rolls around in August, whether due to changes in in WWE's television contracts or simply because it is the right move to make creatively, WWE will find a way to split the titles and give their young talent another stage on which to perform.