Allow in-game mail messages
I'm sure the reason why an actual DM system doesn't exist is because of problems managing spam, as well as just limitations of the UI in general. How about a really, really basic system, where you can create an "item" that you can send to clan members, which'll show up in their item inbox. The "item" would just be a message that they could read.
Why do I want this? Because it is super frustrating to have no way of communicating directly with new clan members. I can't even count the number of people that we've had to remove from the clan because they weren't responding to messages - almost certainly because they just didn't have the right chat window selected, or because they weren't active when we tried messaging them.