The use of wikipedia as an assignment should (and *will* as more teachers understand the value of doing so) definitely receive great support and wide appreciation. The assignment suggested by the article has the following advantages:
1. a real introduction to the community of practice the students are aspired to.
2. a solid contribution to the broader community by the work done by the students.
3. a good motivator for students - the work is REAL and is appreciated by many.
I believe there is ground of improvement too.
Not all academic work and progress are made in a big step. In fact, small steps are the norm. As students begin participation of their chosen community of practice, we should encourage them to take part and contribute in smaller steps. Instead of asking students to submit a whole article (and potentially creating the disappointment of being merged or deleted by the wikipedia community), an equally valuable contribution would be to make positive improvements to existing articles.
If the weighting of the assignment is 40%, students can be asked to make 40 improvements to a broad range of relevant articles (of their own choosing preferably). If the improvement survives after a given time interval (depending on the revision cycle of the article), the point is awarded. Those who made contributions which do not survive the wikipedia review process, they may be given an opportunity by making another improvement to another article etc (time permitting, of course under the current "fixed time" slotted school system).
This change will help to cover a wider range of topics too.