Honestly, I don't need fancy sensors to shut my light off for me. I have a 20 minute commute and my weekend rides are about 2 hours. Put 4 "on" buttons on the thing (30 min, 1 hr, 2 hr, infinity) and that would be more than adequate for most forgetful types.
Bright and cheap sell me. Not having to cycle through to turn on/off is also huge.
My ideal tail light would be a 1W led, super bright, with a built in reflector. one slide switch for the 4 "times", one slide switch for the "mode" (flash, snazzy flash, constant), and a big, easy on/off button. The slides would almost never be touched and I'd only have to ever worry about one button.