Despite what they say in the article, I really don't think they have standing. But I would love to hear why they do from someone familiar with the legal argument.
Basically, they think that the NSA has the ability to index anonymous readers with pages visited, and anonymous editors with pages changed. Then if the NSA is sending that data to a bunch of governments around the word (Egypt, Israel, the Five Eyes, whoever else), dissidents around the world are at risk of being caught for browsing/editing Wikipedia for the crime of being opposed to the government in power.
[1] http://www.nytimes.com/2015/03/10/opinion/stop-spying-on-wik...
That's a big IF and one that will be almost impossible to prove. I don't see how the case holds any merit if they can't prove this happens.