Perhaps along the lines of the Draenic elemental spirits being all "What/who the fuck are you and where did you come from and why are you speaking to me?" where you have to go earn the respect of a powerful Earth, Water, Air and Fire spirit on Draenor. Healing Tide Totem is now Water Elemental totem for all specs. There is that talent for the Air Elemental too. All elementals by default look like the ones we currently have.
In the questline of 4 parts you would have to earn the respect of the 4 powerful ones on Draenor in combat ("Are you skilled enough in combat to deserve me to lend my aid?" style thing ratehr than actual combat).
1) Fire. Power and Destruction. A scenario revolving around fire, and not standing in it while desperately trying to DPS as hard as possible. Not entirely sure, but something that would be very angled towards Elemental spec and would be most easily completed with this spec by FAR.
2) Earth. Strength and Survival. Not entirely sure what this could be, but perhaps one that heavily involves strength and persistence and general avoidance that requires neither damage nor healing, but survival.
3) Water. Restoration and Balance. A healing style one where proving grounds style you must heal a bunch of elementals as they face some enemies or something. Angled towards resto and most easily completed with this spec by FAR.
4) Air. Swiftness and Grace. A movement styled one of flight through the skies trying to catch the Air elemental and DPSing adds which will slow you down on your way but increase your flight speed and ability to remain airborne when killed. Angled to be most easily completed by Enhancement. Think Alysrazor for this one.
A final trial as a mixture of all 4 of these which can be completed by any spec as easily as the other (hopefully there would be a way to do this) that would end in "earning the respect" of the Elements and all of your elemental totems summoning these cool new modelled elementals. I would imagine them to look something like you do when you use ascendance.