Maybe I am not understanding something, but how is this any different than using /castsequence like way back in 2.3 or so? You press a button, an action comes out, you press it again, and another action comes out in a sequence. Is it just that you are happy that a spell sneaks in between spells due to latency? If that was the main thing, then the casting queue should pretty much take care of that. They are saying that you can queue up a new spell before the other one has even finished casting and the server will take out the latency for you.