Considering that the GSL only appears to forbid simultaneous use of the OGL, this idea is kinda crazy. I mean, sure, the OGL is the most commonly used open gaming license, but it's not the only open license out there that is applicable to gaming, nor is it the only open license under which RPGs have been published. There is also, for example, the Creative Commons license, which is much more open and not tied to any single corporate parent. It doesn't sound - correct me if I'm wrong - as if the GSL forbids the use of ANY open license for gaming, just the specific, Wizards of the Coast created OGL.
CC works just fine for most artistic endeavors. People do quite decent business publishing books, art, poetry, recordings under a CC license (I ought to know, I publish artwork under a Creative Commons license), so it's not like CC and OGL are mutually exclusive, or like CC is a kiss of death while OGL means that the game will succeed. And the GSL doesn't seem mention CC (it shouldn't, CC is not a license that WotC has legal control over, unlike the OGL), so you can publish all your non-D20 games under Creative Commons and your 4E stuff under D&D GSL. All it means is that the companies that want to do D&D 4E have to finish up their 3E lines and switch, which is the point of an edition change anyway. None of this halfass one-toe-in-the-water crap. The only companies that could conceivably be harmed are the ones with a heavy investment in 3E game mechanics who don't want to stop publishing 3E-compatible game materials.
One of my bugaboos with the OGL is the fact that a number of game publishers just slapped it and the d20 System onto their games without thinking, "Is this REALLY the best expression possible for my ideas?" This ended up producing a lot of games that are not very good - the d20 System is designed for adventure fantasy, not Generic Roleplaying. Yes, there are some great d20 based games out there - Spycraft for one - but there's also a LOT of dross in the market.