Given the hot debate in the nuclear 9/11 thread, I decided to make some kind of spin-off although a little differently. I don't know if this is plausible (hence the title).
We know that there is a Muslim community in Xinjiang, the Uyghurs, which has been incorporated into the PRC under Mao Zedong. They have been oppressed ever since (although it has definitely gotten better after Mao died) and there is a small terrorist organization there, but it lacks support unlike Al Qaeda. Suppose Bin Laden or some other high ranking Al Qaeda leader gets the wacky idea that these oppressed Muslim brethren need support and need to be freed from the godless communists in Beijing (communists are atheists so its rather easy for AQ to demonize with some propaganda and they don't even have to twist it much). Suppose they hand a stolen Pakistani or Russian nuke (whichever is more likely) or a black market one sold by corrupt officers (who assumed it would go to the US) to the Xinjiang organization. They use it against Beijing in the 2008 Olympics. What happens? Suppose the yield is 25-50 kilotons.
Alternatively, how likely is nuclear terrorism against Russia. The Russians have their problems with Chechen Muslim terrorists. Don't know if they have AQ support, but Russia has some suitcase nuclear weapons that still are unaccounted for and Pakistan isn't known for its tight security or lack of corruption either. Suppose several, three to ten or so, 1-2 kiloton suitcase nukes are used against Moscow and/or St. Petersburg. What then?
EDIT: I don't want any flaming here. I realize how sensitive this topic is, but keep it civilized please.