Troop forwarding like they have in the birthday servers. If someone sends you reins you should be able to forward them to another village rather than having to send them back home to be sent out again.
It's logical, but it does move things even more the defender's way. I'm not sure that's a good thing right now, I feel 99% certain that defence has too much of an edge currently. If that was corrected I wouldn't be opposed to your suggestion.