Attacking your own base and practicing on your friends
I think a cool idea to add in would be able to raid your own base for practice. Find your flaws see how much you can get. Another idea is to add friends and practice on their bases and see if you can beat them. With either attacks you don't gain resources and the training time should be instant and free just for those two attacks.
Attack your clans bases during war prep day
I see that this idea has been passed around already but it would be a great addition to the game. Only available during war prep , there would be no gain for the attacker and no consequences for losing, it would help out clan mates by showing weak points of their war bases plus not only that I'm sure there's hundreds of players who would like to attack their clan mates bases jus to see how they stack up, my whole clan likes this idea, I believe it would be a great addition to the game