I doubt that AQ will be able to pull this off exactly on the astrological event, and I don't get very excited whenever I read another "date-theory" plot possibility. However, I think the article reminds us of the important facet that it's only a matter of time, and every liberal is another potential minute wasted.
Agreed, pulling off an attack like this, nukes concurrently detonated in several cities, would be difficult.
Here's some info on the Mahdi:
http://irshad.org/islam/prophecy/mahdi.htm