Of course all of us who spend too much time on Discord and the forums know that Mischief and Thornblade will be the same rules, launch at the same time, and eventually merge. Get that information out there in a big, flashy post. Maybe even include the line that queues and crowding will likely be less on Thornblade. None of us know the exact ratio of Mischief to Thornblade (80/20? 70/30? 60/40?), but there will be an imbalance. Let's get the goal to be closer to 60/40 than 80/20.
Yes! You have a big article and banner on your website with no mention of it. You have twitter/facebook. Discord. Put it out there, let people know there are 2 identical servers not 1 or you'll just end up queueing Mischief into oblivion and the forums/discord will explode in angry posts with people freaking out. While you're at it strip all the other servers from the preferred list (leave Vox I guess if you want a live server?) So that people are hit in the face with it when they try to log in.