The removal of the core basic attacks in their entirety for the 4 other melee classes implies AA won't be a toggle. True, passive/auto switch has been stated to undergo changes that will make it more fluid, but that's not seamless. In fact it's kind of worse than what we have now, except that stamina would no longer be a factor, by a second or two. This is assuming...
Now: Buff, shoot
Proposed: Disengage, buff, re-engage, wait for AA to kick in (shoot)
What will be: Buff, shoot