I'm not sure that Wikipedia ranking #1 for SEO is due to any significant recent changes on the Google algorithm, I would think that its simply due to it being linked too with good anchor text more and more over time. I don't watch this SERP closely but I would guess that Wikipedia made a gradual climb and didn't suddenly jump to #1 out of nowhere, which might suggest it was due to a change by Google.
Also, this brings up the point of what should the top result for SEO be? Its not a question that has a correct answer as different people are looking for different things. Most people experienced in SEO such as most of us here wouldn't find the Wikipedia page useful, but to a beginner with no idea what it is, Wikipedia could provide a good unbiased definition of what it is.
Basically it is impossible for any set of results to be right for every person, which leads into personalized search which is a whole other topic...
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