The balance of casual is different from main, and games take a lot longer, with a lot more in depth discussion in clan forum when playing properly. Would reset every 9-12 months. At the moment you can start a cw in one season and end it in another. Games started would count for when it was started, with x months to finish.
Would also provide some incentive to see them differently to the more numerous quick cws and actually bother playing them to win.