Since I imagine hangouts based on improving/exploring/experimenting with Barliman, or other similar tools, knowledge of interface design, GUI programming, parallel programming, EC2, etc., should be just as useful as knowledge of logic programming, interpreters, type systems, etc.

I think interest, creativity, and a willingness to learn is the only real prerequisite. For more technical aspects of synthesis using relational interpreters, or whatever, I'll probably do a recap of the core areas of the previous hangout series. I'm sure those 40 hours could be boiled down to something much, much shorter.