My advice is to make the auto-attack a mappable function for any 0-cost skill of the class. For example, Lancer has Light Thrust, Heavy Thrust, Pierce and Full Thrust that do not cost any Action Points to map to your hotbar.

Why not make those abilities "auto-attack capable" with a toggle feature? Add a switch in the Configuration menu that lets you select "Set Hotbar Slot 1 as Auto-Attack Toggle", that allows players who want to have Auto-Attack, to turn it on; those who would not want auto-attack, would turn that off.

That way, if you wanted to use Full Thrust as an auto-attack, all you'd have to do is map it to the auto-attack slot in your hotkey bar when the feature is enabled. This is a very simple solution to a complex and controversial problem. It will satisfy both the pro-autoattack and the anti-autoattack camps.

Yoshi-P, please consider this option as an effective solution to the auto-attack question.