The interesting thing here is that the situation heading into fifth edition is unique--one that the designers of D&D have never faced before.
In the past, regardless of whether it was the shift from OD&D to AD&D, from first to second edition, from second to third edition, or third to fourth, there was one constant: it was D&D, and therefore, it was automatically at the top of the heap. If tabletop RPGs were a race, then regardless of what new engine the D&D car had, it automatically started in the lead position, and generally with a large head-start over the other cars.
This time, that's not true. For the first time in the history of tabletop gaming, D&D will not be automatically starting in the pole position. It won't be starting in the middle of the pack, true, but it'll still have to fight for the lead with another racer.
What's more, it's strongly arguable that the other racer has the head start this time. Pathfinder will be in the position of the established game with lots of product support, while D&D 5th edition will be the new kid on the block that will have to win people over.
Just saying, "It's D&D, it's what EVERYONE will be playing!" isn't going to cut it this time. 4th edition demonstrated pretty conclusively that that's not true anymore. If the designers want fifth edition to reclaim the lead, they're going to have to work for it--it's not going to automatically receive the position just by virtue of being D&D.
It's also not going to be enough to create a game that does the things Pathfinder does...because Pathfinder beat them to it. Open playtests? Nice idea, but it's not going to magically win people over. D&D 5th edition is either going to have to do things that Pathfinder fails to do, or it's going to have to do the things Pathfinder does do so much better that people will be willing to shell out money for it.
And to be honest, I'm not sure they can do it. They have a LOT of problems to overcome. In addition to the fact that they're starting in second place this time around, there's the problem of edition fatigue. When 3.0 rolled over to 3.5, people grumbled. When 3.5 rolled over to fourth edition, people rebelled, and they lost a substantial number of players. Now fourth is rolling over to fifth after only four years. How many people are just going to decide that they're unwilling to keep repurchasing their entire library of D&D books twice a decade or more?
There's also the issue of the fragmented playerbase. The D&D community is severely balkanized at this point, in a way that it wasn't for the last edition switch. Yes, there were still people playing first and second edition, but the very large majority were playing third edition.
Now? There's a chunk playing fourth edition, a chunk playing third edition, a chunk playing Pathfinder, and there are STILL people playing first and second edition. In fact, the last group may well have grown as the result of the OSR.
They're going to have to try to craft a game that appeals to as many of those factions as possible, and appeals strongly enough to get them to switch. Catering to only one portion of the playerbase is not going to get them back to the top of the heap.
I wish Mr. Cook and his cohorts the very best of luck--because, to be honest, I think they've been handed the most daunting task in the history of the RPG industry.