I would hope they keep it optionable in that case. Say you want to take a shot at a random location, you hold M1 and fire - simple as that. But if you're a terrible aim or feel like a more controlled combat pace, you lock onto a target and fire but without losing the option to just shoot randomly at any location.
Honestly, I can see why ranged combat could need some assistance during MMO combat, but I would be sad if that would end up denying us the freedom to just fire volleys into a mass of enemies =)
I'm sure they'll figure it out though.
Off-Topic: Post 1000! xD