Clan-mate "Skirmish" Battle
I think it would be cool if you could have a "skirmish" with your clanmates. For instance, if I had just redesigned my base and I wanted to see how some of my more experienced clanmates would attack it, then if they were willing to spend some elixer on troops, and if I agreed to lose some resources in return, they could attack my village so i could test my defenses - like a practice skirmish!
I think the requirement to have both parties to agree to the skirmish is essential, based on the volatility of some clans without strong leadership... but for the clans that have great cohesion, this could be a great way to increase the feeling of teamwork and self improvement. The resource cost shouldn't have to change to train troops for a skirmish, but maybe there can be a "terms" screen that both parties have to agree to before a skirmish.
For instance, if I were to attack my clanmate with 200 lvl 4 archers, then even if I wreck him/her and get 100%, perhaps I only drain a fraction of the cost of the troops I used. It takes 40,000 elixer to make 200 lvl 4 archers - so if I get 100% on my clanmate in a skirmish, maybe i only win back 10,000 elixer...or maybe 5,000 elixer + 5,000 gold? I dunno, that stuff is more of a Supercell staff decision, but the idea that you can help your clanmates develop and fine tune their defenses in a skirmish battle is something I think people would love!
Also, I don't think there should be a trophy penalty for skirmish battles among clanmates. The idea is to use the system to learn and build, and you'll already be taking a resource hit for skirmishes too, so trophy loss would be excessive in my opinion.
What do you y'all think? Would any of you like to help fine tune the soldiers in your clans by testing your mettle against them?