Saw a post by everyone’s favourite Greedy Goblin, which had an excellent tip as Cata Prep. TLDR is complete but do not hand in as many quests as you can; and when Cata launches you’ll be able to do a quick hand-in and jump start leveling.
He also suggested saving your hearth to a city on the main continents, rather than Dalaran as the portals will be removed. I am not sure where the new 80-81 quest hubs will be, but a major city is a good idea till we do.
Sometimes that goblin is darn clever. Go read for his other prep thoughts.