The only way this can ever be a problem is if Jimbo decides to have Wikipedia sue Citizendium based on ego and personal spite, and I don't think he's that spiteful, and I'm not sure he could convince the Wikimedia Foundation to do it. And by golly if I ever see a banner saying "Wikimedia needs your contribution to fund its continuing legal struggle against Citizendium" you can't expect much in the way of contributions from _me._
You appear to be under the impression the copyright in question is Wikipedia's or Wikimedia's. It's not - they own hardly any of the stuff on the sites.
Indeed. If Citizendium are to be sued over this, it would be a class action suit brought by a large number of Wikipedians. The fact that Citizendium are specifically talking about trying to make sure we can't use their work but they can use ours goes against the spirit of the GDFL and Wikipedia (which is all about collaboration), and that may well piss of enough Wikipedians to make a class action suit viable (it doesn't really take many, as long as one of them can afford a good lawyer).
According to Wikipedia, the minimum statutory damages are $200 per work (and that's assuming Citzendium can claim good faith, which would seem unlikely, in which case it's $750). What counts as a work? Each edit counting as a separate work would seem unlikely. Each article counting as a separate work would seem more likely, but how does the money get divided up between contributors?