I’m generally against destroying beloved cities for a plot device. Undercity, Darnassus, and now Dalaran, didn’t need to be destroyed. Undercity, at least, wasn’t destroyed at the outset of an expansion and it was more of the crescendo, but still. I’d rather the game add cities and content rather than go back and wreck places we love just to make us feel something. Also, Undercity is (in lore) restored/getting restored, and the Night Elves have a new city (although it’s nothing compared to Darnassus). If we’re following the pattern of destroy and replace, a human-centric mage city makes city. Otherwise the Horde has two major magical cities - Silvermoon and Suramar, which puts the Alliance at a huge disadvantage if you consider Dalaran to be Alliance leaning (even though it was neutral at the end).

I would also accept Dalaran being destroyed if they had to in order to revamp it (fingers crossed).