Leader-to-Leader Private Message
I get why player-to-player private message doesn't exist. People can be immature, it would get messy and add a lot of server traffic. However, limiting it to just clan leaders could prove to be a huge improvement in player communication and clan strategy.
Leaders can discuss merging clans, feeder/sister clans, share raid/defense strategies that work/don't work, etc. Having the standard private messaging functions (mute, block, report, etc.) would probably be necessary. Possibly limiting the clans whose leaders can be reached could also be beneficial. Example: leaders can only contact other leaders whose clan trophy score is within 500 of their own.
Let's discuss and throw some ideas around.