Personally, I'd love to see Andy Richter or Michael McKean as a successor. They're both suuuuper sharp, and probably the best ever Celebrity Jeopardy! contestants.
Andy Richter would be fantastic. I wonder if he could stay on Conan or if that would be too much of a workload.
The travel would be the problem. Conan tapes in New York and Jeopardy is in L.A.
Conan is based in LA now as far as I know. He moved from New York to LA when he got The Tonight Show. Then when he was fired, he stayed in LA. He then got the TBS show which is still in LA.