As I see it, an OGL-style license could be invaluable to a D&D edition that aims to cater to players of all previous editions. I doubt Wizards has experts in all previous editions of the game. As much as Mike Mearls GMs the original edition once a week at Wizards headquarters, his experiences are certainly tainted by the first edition of D&D he played, by his personal tastes with regards to D&D editions and, certainly, by the fact that he worked on 3.X (a little) and 4e (a lot). The same goes for Monte.
Third party publishers, on the other hand, can gather a couple of experts for any given edition (even obscure variants) and get those people focused on adapting their experience to the new rules. It is easier to publish products with very different feels and catering to a more varied audience this way.
That could also help Wizards determine what modules of optional rules to launch next at any given time. Observing the market and what publishers are more popular. Even incorporating rules from 3rd party (which, surprisingly, they rarely did in 3.x).
Should the 5e project be a success, the market will be large and diversified and I really see this as a winning approach.