Ordering is something that I'm not sure about (but I've myself been thinking about it for a future addon- if not the current one) that would 'weigh' the URLs like .edu/wikipedia etc. much higher. Would such a feature be helpful to you? And as a part of the same addon?
As for only results from specific websites, you may use Google Operators (like inurl, site, etc.)
Yeah, I'm looking for something like this too. I would like to have Wikipedia at the top of the results.