I can think about six explanations for this story.
1. Bush has gone through is last election and Rove wants to get on to fresh pastures.
2. This anonymous insider is one of Rove's rivals for the inside track.
3. Some other insider is trying to push Rove out.
4. Bush is getting tired of Rove.
5. Bush is sending Rove to manage the campaign of his replacement in the White House.
6. This reporter is mistaken.
7. This reporter is lying, and made the whole thing up.
Oops, that's seven. And I could probably think of ten more.
Among the possible explanations you list for a rumored departure of Karl Rove as the White House political advisor, I'd be willing to bet my life that #4 is NOT the reason.
President Bush is a smart man and a keen judge of personal character. Karl Rove is still the most competent and clever political advisor on the American scene today. A good executive never grows tired of a brilliant and loyal employee. He does whatever is necessary to maneuver top performers into jobs where their skills are best utilized.
If Rove is indeed making a move, I pity his next opponent.