There already is a customizable auto-sort (starting a new tab with different item types, sorting based on level, ilvl, etc,). I can understand why this is a problem for you and a small number of other people perhaps, but personally I hit the sort button about 2 dozen times a day and don't want to be bothered with an 'are you sure?' dialogue, though I suppose having an on/off toggle for that would work pretty well for both of us.