I would say that 5E will not have an OGL. What it will have is one of the following:
- Much less restrictive GSL, drafted with the goal of bringing a lot of 3PPs back into the fold. The core PHB stuff will be off-limits, but monster and magic item statblocks--pretty much everything you need in order to create a good adventure--will be open for use, and companies won't have to worry about having their license yanked out from under them.
- GSL so restrictive nobody uses it, or no GSL at all.
The first option is what WotC will do if they are smart. Hasbro isn't going to stand for a re-creation of the OGL; the execs will say, with some justification, that Wizards set itself up for the 4E/Pathfinder split. Opening up the core of the game achieved Dancey's goal of "saving D&D" so that it could never again be threatened by corporate mismanagement, but it's not clear it was good for WotC's bottom line even in the short term.
But a more licensee-friendly GSL, drafted to keep the core of the system off-limits while opening up the rest, would enable Wizards to "outsource" adventure development. This is a vital support task, which Wizards has never been very good at and which has never made them much money. Letting 3PPs handle it for them is just good business sense, while they focus on their core competency of building the game itself. It would also buy them some community goodwill. I think the importance of this goodwill is widely overstated, but it's not worthless.
On the other hand, media and publishing companies don't have a good track record when it comes to opening up their IP, even when it's clearly in their interest to do so. Witness how record companies have had to be dragged kicking and screaming into the digital age. It's quite possible that Hasbro and WotC executives will take Pathfinder as evidence that opening up your property just comes back to bite you in the long run, and the answer is to clamp down on everything. If that's the case, 5E may not even have a GSL. If it does, it will be as bad as or worse than the present one; no major 3PP will touch it with a standard-issue ten-foot pole.
(To the question of whether Pathfinder would have happened if 4E had had an OGL, I agree with those who say Paizo wouldn't have done it, at least to start with. As I recall, Paizo was planning to go to 4E, but the complete bungling of the GSL release forced them to take a different route. However, I suspect
somebody would have set out to snap up all the discontented 3E players. After all, under the OGL it's literally possible to reprint the 3E Player's Handbook, absent a handful of names.)