I think it's a nice idea for older hardwired systems, congrats!
I do think your window is rapidly closing as we approach the "connected home" era. Nevermind, it's here. I think you've still got buyers out there who could spend this small amount of money to add features to an existing system, though.
Just remember that for about $1000 I can buy an alarm and some cameras and when the alarm goes off, it will flash the lights, call me, text, and email me a picture of anyone or anything that triggered the motion sensor, and adjust the temperature of the heated floor in the bathroom.
