Re: The Singer not the Song
I don't think that filter makes much sense because just having the term Wikipedia in a search doesn't mean that the user wants Wikipedia articles. For example, if I search for "Wikipedia funding", I probably don't want Wikipedia's article on the concept of funding. I might want the page on how to donate to Wikipedia, which isn't on wikipedia.org because it's on wikimedia.org. I might want Wikimedia's charitable tax filing. I might want one of the numerous news or opinion articles about donations to Wikipedia. By interpreting all uses of Wikipedia as preferring searches on it, I'm likely to produce worse results for any meta search like that.
The same is true of many other terms. For example, if I look up "Google data collection opt out", I'm more likely to get useful information if news articles or pages about privacy than if it sorts by site and gives me twenty Google corporate pages first. Substitute any other company and I think you'll quickly find examples where you may want information about them rather than information from them. If you really want to limit your search in that way, the site: tag is available to make that filter explicit, so rather than assume for you, something that usually gets worse results, it would make more sense to make sure people know the option exists and can use it when it gives the desired behavior.