the only new thing in a5 compared to a3 was longer drain intervals. which already people are skeptical about, stuff like 20-40000km drain intervals.
compare a1 and a5 they are 90% the same, look at the technical sheet, only difference is for engines which use low viscosity oils with a high shear viscosity and run on high temperatures coolant temps, technically the only difference is shear rate viscosity of A1 was 2.6 to 3.5 mPas.s and for A5 is 2.9 to 3.5 mPa.s. not a huge difference so thats why they are not common. mobil 1 oils have been a staple for many years so they haven't really bothered changing them, infact very few oil manufacturers are using this standard.