The one reason why I don't think we'll see an OGL as open as the 3rd edition one is that I don't think WotC would want a game that allows a 3PP to create a game like Mutants & Masterminds out of it-- a game that was based upon the rules and trappings of D&D so you got a bunch of people to buy into trying it out... but was different enough from it that you didn't have any reason to buy the D&D Player's Handbook to play it.
So this ended up being a genuine case of WotC creating a market and a marketing campaign for Green Ronin that didn't actually net them any money. Green Ronin created a 'D&D superhero game' that you didn't need D&D to run.
Any OGL or GSL in the future will keep that kind of thing shut off. And if they can't shut that kind of thing off... then I don't think they'll have another OGL/GSL.
Bleh. I think it's been said before, but I'll say it again. Mutants and Masterminds
is still good for D&D. This is the point Ryan Dancey keeps making. Games like Mutants and Masterminds don't actually compete directly with D&D. For D&D players, M&M is a pleasant diversion and an example of the diversity possible within the d20 system. They're already branching out, so they're likely the kind of players who will try all kinds of stuff, from western gaming to Call of Cthulhu to variations on modern gaming, and in the end, D&D remains the biggest fish, so they always come back to it. They always stay interested in what D&D is doing, because that's the core of the hobby.
Meanwhile, M&M brings in a whole new type of gamer, because it's a superhero title, comics fans who aren't already D&D fans, are likely to pick it up. Now, maybe that's the extent of most of their forays into RPGs, but some of them will be intrigued and move on to the core of the hobby, into D&D. That means new long-term customers for WotC, and they didn't have to take any of the risk of publishing a superhero RPG. If anything, M&M is a free marketing campaign for WotC by Green Ronin, not the other way around.
But what if M&M makes tons of money? It's true that WotC will be missing out on that cash, but they wouldn't have got any of it anyways, since they never planned to make a Superheroes RPG. But WotC technically owns the core of d20, so after M&M proves lucrative, it's very easy for them to make a competing superhero game, if that's what WotC decides they want to do. Green Ronin took the risk of pioneering the market, and now WotC can capitalize on it, if it turns out to be lucrative.
I don't know what the current WotC management is thinking right now, but if they have the kind of mindset that seeks to shut down M&M, they're only hurting themselves.
That being said... there actually is one final way (as was touched on above) that I think WotC might be willing to open things up-- by charging fees to the 3PPs and/or customers to include OGL content in the DDI tools. If they could charge players like an extra .25 a month to their DDI subscription to "unlock" 3PP customized character generation content in the new Character Builder (or likewise charge fees to include new 3PP monsters into the Monster Builder) maybe that would inspire them to open up the OGL. Because at least then they get some money out of the people who don't want to buy the WotC products and buy the 3PP products instead.
I'll never say never on that, but I don't think it's the right way to go. Not because I think the price point is off, but because I think it's a barrier to convenience. My problem with microtransactions is that there is an inherent cost in convenience in requiring players to sign up with credit card info. Kids are a big part of D&D's market, and credit cards are still something that not all of them have.
