That might be completely stupid, but how would a system with one turnchat a week (probably on a WE day) and still 2 or 3 turns a day the rest of the week work ?
This would make the game faster, lessen the problem of timezone (easier to be there on week-ends), and still allow for once a week "global discussion" which looks fine. Then again, I'm pretty new to that so it might not be feasible.