Come up with a compelling argument that will convince WotC corporate, their corporate parents at Hasbro, Hasbro's shareholders, and the lawyers that the OGL (or something like it, tailored to 5th) is good for them.
I think it's a pretty tricky task to do so, when anyone can look at D&D's primary competition and see that the system that the company is selling is one that WotC developed and then gave away under the OGL.
The last thing I expect that they want is for five to ten years down the line, when they're going through all of this again, to find themselves competing with a second system that they gave away. Especially if Pathfinder is still going strong.