Nemo - follow up question, is there a published case study anywhere in any language?
I am not aware of WMF legal ever getting involved in these sorts of cases. Chasing copyright violations or managing a project to defend against copyright vio seems more like a project for any Wikimedia chapter or community organization to do, perhaps with WMF grant funding support. Comparable organizations like YouTube, Facebook etc also do not provide direct legal support to their user base and I cannot imagine the wiki community and WMF coming to any agreement for doing this either.
I know there are lists on English Wikipedia or somewhere of instances of publications plagiarizing Wikipedia text. I am unable to find the links right now, but I have seen several compilations somewhere. I am not aware of any of those cases going to court either.