Just a general response:
Wikipedia, being one of the top 10 websites on Earth, has enormous power. People are not going to go to a Wikipedia page and see a video and not want to play it. "A highly trustworthy site is using a video format that I can't view. I'll just give up".
No, they are going to follow the link "If you can't see this video click here" and install the viewer. You just then need to get some video into some mainstream articles. Wikipedia then has just single-handily expanded the install base for Theora, and it's down the slippery slope to widespread adoption.