(3) Another debated use of service=alley
started up in this post, specifically for ways too narrow for most 4-wheel vehicles but still legally allowing small motorized ones like motorcycles, rickshaws and micro car. While these pathways are rare in Europe, they’re really common in Asia.
Some people think all motorized ways should be classified based on their main function, regardless of width, while others think this should only apply to motorcars and larger vehicles. There’s no clear consensus on this either.
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=alleyway
fits better to solve (2) as you suggested.