Its a great idea, but it needs some tweaking! Like a requirement of you to have to cover the proximity sensor for at least 3-5 seconds before it activates, atm just trying to swipe to close a text conversation can initiate a call! Disabling it for the time being, until a setting for a time delay is implemented
You can do that already... press the silence button when it is ringing, that will be replaced by an SMS button, press that & your prepared message is there, with recipient populated just waiting for you to click send...