It probably would have been Bill Richardson, except for this.
James Fallows speculates that Clinton's presence may have something to do with the Box in Myanmar, as well as the two reporters being held in North Korea.
I'm sure it does, but perhaps only indirectly.
Part of North Korea's gripe is that it wants higher-level attention from the United States. Bill Clinton is pretty high up, although his position is not official. However, North Korea's fondness for that other Bill was independent of his stature in the US government. And Clinton did manage to negotiate the 1994 Agreed Framework, which George Bush trashed.
But North Korea has also been making noises about formally ending the Korean War, and Bill Clinton's charm is unlikely to make those noises go away.
His status may give an opening. It's unlikely that he was sent without consultation with the North Koreans.
Update: That was fast. The two reporters are said to have been pardoned. And I wonder if Russia and China have been talking to North Korea behind the scenes.