Smaller groups I agree with; our group ended up breaking into two subgroups. Tic tac toe I think was actually not a bad problem - most groups opted to do something bigger than time allotted with Om and other frameworks, but at the core it was actually a small enough problem to get all the basics done and working in the repl, at least for me.
On a related note, it seemed to me that most people wanted to get their hands wet with specific libraries. Maybe it would be worth voting on popular frameworks to work on for a session?
Team coding was a challenge, I think figuring out something that can be cleanly decomposed might be the best way. Perhaps a web application and each team works on an endpoint or utility function?