Wouldn't mind them adding in a catch up mechanic.
Example: Anyone who has a castle level that is 3 below the highest castle level gets production/building/training/experience bonuses.
All bonuses scale with how close you are to being caught up. So the further away you are from the threshold, the higher % bonus you get, the closer you are, the less % you get.
This is also a great idea. A kind of catch-up mechanic like this would make playing in any server relevant, even as a beginner in an old server. And it means whales going too ahead would end up triggering the bonus for others, creating kind of a balance.