Druids during Wrath of the lich king were in my opinion the best one.
We werent the best dps when it came to aoe but on single dps and 2 target's dps we were quite strong. People brought druids with them for not just their dps but mostly for their combat ress/buff and most importantly the innervate. Innervate could give a healer their entire mana back, because of this healers would whisper me for it. There was also the fact that any druid could do a tranquility for a big healing, the druid could also tank for a while which could save the raid. Ferals required to be behind the target for shred was something that was quite nice, it added some complexity in the form of positioning yourself right.
The druid was a true hybrid in wrath of the lich king.
For the druid to be a true hybrid class it would mean that many elements need to be taken over from wrath of the lich king. It doesnt have to be that we become dps gods or tank gods or healing gods, as long as we become a support class since that is what druids are. Imagine that blizzard makes druids the only support class and people start recruiting people who arent just good at their spec but can also contribute to the raid because they are good. Make some spells that a druid can use to support the raid depending how good he is doing his job. For a dps it would mean, good dps means big buff for couple of seconds in healing or dmg or reduced dmg or increased speed or increased spell casting etc etc.