However, I’m not convinced that (2) and (3) should share the same tag. @dieterdreist initially proposed this with (3) in mind, but I agree that in terms of naming,
highway=alleywayfits better to solve (2) as you suggested.
I think 2 and 3 are the same, because ways which aren’t narrow (lanes=1, which means a full sized lane) are highway=residential. I think alleyway is for lanes=0, but I am open to discuss loosening the definition to include narrow streets where a motorcar could barely pass, with no to few lateral space, as it is still a heavy impediment (pedestrians have to step into entrances or press themselves against the walls)