Well, what the heck, might as well chime in.
First of all, WotC is to D&D what Microsoft is to Windows. Sure, they tried the open source thing, but I'm not so sure that it panned out well enough for them that they want to do it again with 4E. Keep in mind that this is all speculation, and at this point in the game I have no insider knowledge.
Now, my prediction for 4E is that we'll probably see a game that is easier to learn and streamlined so that combat moves faster. Let's face it, even Ryan Dancey said that D&D was a half hour of fun condensed into four hours of actual play. Let's also face that facts that between WoW and Neverwinter Nights, there are D&Dish experiences out there that allow people to adventure with groups of other people, with fast moving combat, and pretty incredible graphics (just got my copy of NWN2 today. Wow!)
So if 4E is a streamlining of the system, and it isn't open game content, I think that a fairly large segment of the gaming population is going to ask for another option. In the computer world, it's called Linux. Hey, what do you know, we already have that with the OGL. Sure, they can yank the D20 logo license, but so what? The OGL allows game publishers to create new games using pretty much any rules they want to create, but it is expected that they will be derived from D20.
The OGL will continue to exist, though following WotC's lead, publishers will probably morph it into a system that plays faster. I expect that someone will release something that people will like and will be 100% open game content, and then other publishers will run with the ball. I think Green Ronin has something pretty close to that right now with True20, though I'm not sure that a large number of people are willing to embrace all the mechanical differences in that system, such as the loss of hit points.
So when this brand B comes along, and it is widely supported by third party publishers, WotC will effectively be competing against its own prior success. The market will probably follow D&D 4E, but I could see this as of yet unseen new system gaining a pretty good following, and one day being the preferred system among the serious gamer geeks.
As for my personal opinion, I'm going to watch and wait. If 4E is an improvement over 3E, and it doesn't try to revamp what roleplaying is by turning it strictly into a miniatures game (the very thing the game morphed from to begin with), I'll check it out and I might even switch my home game to it. If I don't like it, and there's probably a 50% chance of that, then I'll start looking into OGL alternatives, possibly even helping push for that third party streamlined standardized initiative.
