My thought was actually to have multiple projectors per block approximately 10 feet up (building mounted) with sensors to identify people and have them 'place' a smallish ball of light at about 8-10 feet up that floats above and in front of them, but with much less light needed than a 'street light'...and maybe stationary one's in intersections (these could even have 'covers' to stop wasted light from going up). Or, it could project tiny lights (like in the video) near ground level to illuminate the sidewalk, but that's not as useful by far.
By my estimation, there could be less pollution because there would be fewer, smaller lights on at any one time (where normal lights are just ON all night). I agree, there are many issues to solve, but it's doable if thought about thoroughly.
It's a little too late to worry about 'light pollution'...in fact I bet it's not on the average person's radar. Sadly, many people in cities have never seen stars at night and don't have a clue how much is hidden from them. (I live in the boonies of far N cali, and we still have light pollution from nearby towns, but nothing like in a city...I've even watched the international space station get re-supplied while sitting in my hot tub! That was amazing!).

Tags for this video have been changed from 'foo fighters, walk, dave grohl, song, track, wasting light' to 'foo fighters, walk, dave grohl, song, track, wasting light, Falling Down' - edited by youdiejoe