Cross realm dungeons are a very good thing. If you've ever logged in at times when no one is on, such as as I'm writing this (10:40 CST), you might have noticed that things are quiet. Too quiet. That's the sound caused by 90% of the player population being at work, school, or unemployed and already too drunk to remember what a computer is. The remaining 10% are 90% bots and 10% sick people, 'sick' people, and unemployed who can no longer afford alcohol.
This makes it very hard to form a group based on only the population of a single realm. To make it worse, a low population or highly imbalanced realm can be like this all the time. So clearly forming groups across servers will help get things rolling.
But there is a problem: It's on all the time. When it's 8PM and approximately the population of Greece is online at the same time, it is not hard to form groups from a single realm. At that time he cross-realm ability is unnecessary and serves only one function: to group up people who will never meet again and therefore have zero interest in each other or their reputation. Cue ninjas, assholes, ninja-justifiers, and more assholes.
Add a few seconds to queues. Use this time to delay group formation to see if players from the same realm will appear. As players come on, shuffle the order slightly to group up players of the same realm. On average queues would be unchanged, pushed up sometimes, pushed down sometimes. On average groups would have more players from the same realm.
This system should have three goals. First, use the cross-server element when needed for rapid group formation. Second, keep the group formation tool for convenience and speed. Third, bring together players of the same server more frequently without removing or ignoring the previous two goals. In other words, telling people to use trade chat isn't the solution.
P.S. If you read my blog obsessively like I do you might have noticed that most of this is copied from an older post. I did that because starting a post with a Godwin's Law attack on subatomic particles often distracts from the actual point of the post.