I like JR as a commentator. He's the best of all time and is excellent as the Voice of RAW. He still has the skills and as long as he has it, and doesn't get stale I don't think he should move from there. His chemistry with Lawler is great too.
As for JBL, I think it would be a great fit. He's excellent on the mic, and would shine in an authority position. Especially being a heel GM as Teddy Long is the face GM. Plus an angle can be made out of it, where JBL gets pissed off at Teddy for a lack of money as a commentator. He can say that he is going to the big leagues and big money at RAW.
Then Coachman can go to Smackdown as a commentator. Unlike many other people, I think Coach can make a great heel commentator especially with Michael Cole. I think their chemistry would be great.