If that's the case, then obtaining the students' consent to release their Wikipedia username (which could be a random string of characters with no identifying i

If that's the case, then obtaining the students' consent to release their Wikipedia username (which could be a random string of characters with no identifying information) needs to be a precondition of the students' participating in the assignment. If a professor has 1700 students start editing Wikipedia and 85% of them are plagiarizing, that's a huge burden to place on the Wikipedia volunteer community to clean up. There are a limited number of volunteers who handle copyright and plagiarism issues and it is unfair for a professor to increase their workload without giving them information about which users are making changes that need to be scrutinized. The problem here is that the professor has refused to engage the Wikipedia community and has, in his own words, gone underground.