I would like to see a system implemented like this:
Clan wars are started between two clans (obviously). Once started each player has the chance to attack 3 times a week. Once a player has been defeated 3 times, they can no longer be selected as a target for attacking.
Each battle you win, you gain a star. You can choose from online players in the other clan to fight. The clan with the most stars at the end of the week are the winners. If a player refuses a battle from a clan fight, they will lose one star from their clan collection. This includes time-out, so players can't just close Supermechs once they are challenged to dodge the fight.
The winner will be rewarded on the level of the enemy clan. For example a defeat of a level 1 clan could be 120k SM split between its players (10k each if you have 12 members). As the clan level lowers, the reward is lowered.
Above is a simple layout to visualize it.
Green tick: Player is online and can be challenged
Question mark: Player is offline
Block: Player has lost 3 times and can no longer be challenged
Attacks left: How many attacks you have left
The Boxes with green dots in are the stars (I couldn't be bothered drawing stars). When lose a star is added against your name. At 3 stars you can see a player is blocked, meaning he has lost 3 times. The total of these green dots (stars) on the enemy team is how many stars you have.