This short story they posted actually does explain a lot of the details that make 4.3 hold together. If you can get through, it helps a lot:
http://us.battle.net/wow/en/game/lore/s ... -aspects/1
It explains:
1. How they can take the Dragon Soul from the past and not screw things up.
2. Why we start by going into the future.
3. Why the Dragon Soul even works on Deathwing (it shouldn't).
4. Why Thrall is so important to the endeavour.
There are even a few tidbits that hint at future events (you can spot the MoP foreshadowing really easily).