That could be a great idea, but I would think it could be a small delay people who want to get straight to dictating their wishes won't appreciate.
As one who has fun with the unit quotes in Starcraft, it's be cool though.
Or Cortana could at least call you by name other than when you ask her what your name is. There is a toggle that asks whether or not Cortana should greet you by name.
I would love her to call my name when I long press the search button too!
And imagine how cool will it be if she calls your name when new notifications come in. For example, "Ahem, sorry to bother you Jake. You have a message from your boss. Would you like to read it or ignore it?"
It would be neat as an option. I personally would not like it. I would prefer as little a delay as possible. Also, while I can whisper and have her make an appointment without bothering my officemates, if she talked out everytime I held search I would really need to have her turned down all the time.