Since 2001, the World Title was unified, then de-unified, and unified once more. Another de-unification would be awful for the World Championship. Either there's one World Champion, or there isn't any.
With the WWE and the World Heavyweight Championship, they were held on equal ground for a while, but starting in 2008, the World Championship was treated more like the Intercontinental Championship of old, with guys who were not quite top talent getting an opportunity to hold the belt, or up-and-coming wrestlers who would be groomed to one day hold the only title that mattered, the WWE Championship (CM Punk, Daniel Bryan, etc.).
Having two world championships once again would most certainly re-create that dynamic once again. If WWE wants to have brand-specific championships, they can have the U.S. Title be on one show and the Intercontinental Title on the other (apparently, Daniel Bryan had this idea when he won the Intercontinental Title at Wrestlemania 31; he wanted to defend the championship exclusively on Smackdown). But the World Champion should remain one champion.