I found out that if you use the toy "The Schools of Arcane Magic - Mastery" while in the new Dalaran, it gets you in the same rooms as in WotLK, but in the new version, there is a door that is only interactable if you're a mage from what I've seen (tried with two of my alts, a warrior and a rogue, but both are not 110 yet, so that might be related?). When you get outside, there's a ledge, from which you can jump and get into another small room with multiple NPCs. That might be something to look into.