You play a game with pedo-bears, metro-sexual musclemen, and cat people. There's nothing immersive about it unless you imagine yourself as part of some manga comic.

I'll reserve judgement till I see it in action, but every single MMO that has had casting interrupts while moving has been an annoyance rather than some engaging gameplay mechanic. You can pull off far more interesting things being able to move using abilities than playing red light, green light.