I'm not totally clear on it either, and I've played WoW solid for 10 years.
It may be a reference to Blackwing Descent, a raid from Cataclysm. There was clear evidence that there were experiments going on to merge the dragonflights (similar to seeing the dragon corpses and Chromaggus in Blackwing Lair). There was also a revived Onyxia fight, a la Frankenstein with lightning to boot. Finally in a paused screenshot from the trailer there was a legendary magma worm card, which would appear to be the boss Magmaw from Blackwing Descent.
Taken together my guess is that it may have some reference to that raid zone.
I'm not totally clear on it either, and I've played WoW solid for 10 years.
It may be a reference to Blackwing Descent, a raid from Cataclysm. There was clear evidence that there were experiments going on to merge the dragonflights (similar to seeing the dragon corpses and Chromaggus in Blackwing Lair). There was also a revived Onyxia fight, a la Frankenstein with lightning to boot. Finally in a paused screenshot from the trailer there was a legendary magma worm card, which would appear to be the boss Magmaw from Blackwing Descent.
Taken together my guess is that it may have some reference to that raid zone.