I believe that the original poster is very close to having this capability in something he is developing, and intends this as a tease. I would have preferred he just say that instead of pretending to be someone asking a legitimate question.
That said, let me reiterate that I think there would be much interest in this. I am currently wrestling with BigTalker, VLC, VLC Thing, smart apps, installing additional speakers, etc. when what I really want is simply an API to call to have all Alexa devices in the house say something with no prompting. So far, the closest thing is to raise a notification which must be asked for. If the house is burning down, I’d like Alexa to just scream at the top of her lungs “Get the f out of the house!!!” rather than turning on a message indicator.