It is possible that the Development Team is taking a page from Marauders, in that they could utilize Stances to automatically switch on and off auto-attack.

Excuse me while I talk off the top of my head here.

Archers (and Musketeers) could have an ability called "Sniper Stance" which triggers when no hostile enemies are within melee radius of them. When that condition is true, their auto-attack switches off. They could probably throw in some other benefit, like some sort of TP gain or enmity reduction, but I won't go into that, because I'm just brainstorming right now.