Y and S are full fare economy on shorthaul.
U and L are full fare new-economy on long haul.
Presumably, this in the new wording to allow upgrades from:
1. economy to business in shorthaul
2. economy to new economy in longhaul
2. new economy to business in longhaul
In shorthaul, a Y class ticket (so called Business Economy) will get you a seat up front. Not sure if this applied on longhaul services. Anyone?