You could probably even make a 5E Neoclone under the OGL even if 5E itself is not released under the OGL. This very well could be something WotC/Hasbro would challenge in court, but would they win? I'd only risk it under specific circumstances and in specific jurisdictions though.
An exact clone would probably be out of reach. But, a game that's fairly close would be doable, unless they go further afield of editions 0-3 than it would appear.
Thanks to the OGL, new versions of D&D are constantly appearing. And gaining traction. A few years ago, who would have thought that a 2nd wave clone like LotFP would achieve the kind of visibility it has? Now, we have ex-WotC alumni, like Mr. Tweet, jumping in to what was once referred to as the "fantasy heartbreaker," market. They may be, or remain, niche products. But they aren't all heartbreakers, anymore.
More rpg's like Goodman Games'
Dungeon Crawl Classics, will be published. Games that take the bare bones provided by the OGL and turn it into something very different.
The OGL and the Open Game RPG's, derived therefrom, d20, retro-clone, or other, aren't going anywhere.
The desktop publishing genie is out of the bottle. Creative, resourceful gamers and DM's
have gotten a taste for it!
The last time WotC eschewed the OGL, they lost the support of a lot of 3rd party publishers. The number of whom, has grown quite a bit over the last 4 years.
And many of those publishers, are arguably better designers than the WotC employees.
The idea of not needing WotC, is now entrenched.
It's not a question of preventing another Paizo. Sooner or later, whether or not 5e utilizes an OGL, another Paizo
will come along. Their game may not be as successful as Pathfinder. But it'll be successful enough that they'll be mentioned in the same breath. There's just too many
good designers jumping into the game, for me to think it won't happen.
And there's a very good chance, that the OGL wave will continue to roll and build momentum. Does WotC really want to fight against it?