There is a popular movement afloat to make this happen and my answer to the question is an unequivocal - NO - NOPE - NEVER!
Stewart has made his Presidential choice plain to anyone even remotely familiar with him and his political leanings. He is, without doubt, an Obama man.
A true moderator must be someone impartial, or at least, someone who hasn't publicly declared whom he or she favors in this upcoming election. In today's sharply divided public I know that someone would be difficult to find (the Republican Primary debate moderators certainly proved that), but a legitimate, qualified moderator is out there, somewhere.
The last thing we need is another publicized showboat fiasco led by someone of Stewart's caliber just to ensure some network a substantial ratings pool.
This is an election (likely the most important since the Great Depression) for the highest office in the land, the leader of the free world, and the most powerful political position on Earth - not an episode of Survivor or American Idol.