I'd be interested in a setting to have Siri listening all the time while plugged in to a charger and having a voice command act as holding the home button. So, the classic Star Trek interface of "Computer, <insert question here>", although presumably you'd want to address it as Siri as I can see the word computer coming up a lot in conversation.
I'm surprised no one has asked for it to be activated by a double-tap on the phone body, that the accelerometer could recognize.
Then you could keep the phone inside your shirt pocket, and just tap it as if it were a Star Trek comm badge... with of course a futuristic beep coming back as a prompt