Definitely believe Apple had been exploring sensor driven UI effects if you follow the signs like this patent [0]. Wouldn't have been shocked if they'd had a prototype with the whole UI doing it around iOS 4/5. But only the Music.app volume knob part shipped (iOS 4 IIRC the brushed metal on the knob had a tilt based lighting effect).
[0] http://www.google.com.pg/patents/US8130237