In Dragon Annual #6, released in 2001 (around December, I believe), Ryan Dancey wrote an article titled "What the Heck is a d20 System?" In it, he talks about the genesis of the both the eponymous game engine itself, and the OGL and d20 STL. As part of the article, he says:
Later on, he says:
Now, to be fair, he also admits:
So while there was certainly an expectation that these network externalities would ultimately benefit WotC (i.e. the Skaff Effect that Dancey mentions elsewhere, albeit not in that article), there was very much an understanding that entirely new RPGs could be created from what WotC had made available under the OGL.
For what it's worth, the bio at the end of the article mentions Dancey no longer being with WotC, so it seems like he wrote that after leaving the company.