Either that, or add their target into the enemy list. That would involve more screen clutter, but would have the advantage that you'd be able to see who any of the mobs are targeting, not just the main boss (or whichever you have focused). That way you would know and could react to times when one of the adds breaks off from the tank to target another party member. Currently, only the tank and the wrongly targeted player see that based on color of the enmity icons.

As healer, it'd be nice to get a heads up that another player may need a heal, and as DPS we'd know when an add turns to attack our healer. (I know I for one, when DPSing, try to prioritize any mob that does that, but can currently only see it if we're spread out enough that the mob clearly moves towards the healer. In crowded areas, it's easy to miss.)