It won't be easy to find somebody with his breadth of knowledge to replace him.
I don’t think you need a particular depth of knowledge. You need someone willing to do the pre-work -clearly there are notes from and conversations with the contributors beforehand, someone with curiosity to learn about things outside their areas of expertise. A good journalist would be fine
I always hoped they would do a behind the scenes episode on what they do to create one episode - pre-reading, selection of experts, discussion of questions to ask etc.