This will not only make it impossible to hide indefinitely, but will encourage more active participation (i.e. spending money EA... take note!) for a number of reasons:
• You'll have to repair damage reasonably quickly to get all the rewards.
• Or you just don't get 'bubbled' at all (there wouldn't be a 30min clock until you're under that shield) by repairing before shield is activated.
• It removes some of the power club presidents have over members to make them follow their rules and tell them how and when they are allowed to play under threat of expulsion, which I find appalling. We are all independent players with our own cities and nobody should be at the mercy of another player.
• It will allow you to see a city repairing over time and know when you can hit it. This encourages a player to 'self repair' and come out sooner to surprise the opposition.
• It would eliminate the repairing of all but one damaged building so as to gain all (but one) of the rewards since repairing all but one building would mean you'd be out of your shield in 30mins.
• If you choose to wait out the 6 hours you still have that option and can either forfeit the rewards or try to repair one every 29 mins and still get the rewards while you build up your stock of war items, energy etc., or take time out to sleep, work etc.
• It will make the game more open and fair and ensure that there are regular targets available to hit, at least until the final few hours of the war. Battling (not hiding) is after all, the point of the wars, isn't it?