Parabolic mics pointed at the participants?
Neither parabolic nor super-cardioid mics would work very well in an echoey room. The sound reflections from the walls would still get picked up pretty well.
Wireless body mics?
Expensive. You'd not only need a bunch of wireless mics but also a mixer to channel them all through at the same volume ratios to the person/people at the other end. Personally, I like the "talking-stick" mic idea. It'd be a great way to manage the dynamics of turn-taking in conversations that some people seem to have difficulty with.