What I'd like to see is a Cata-style, but even bigger, world revamp. Bring
all zones to the present (so that level 1 players don't, say, have their intro quest telling them that Garrosh is Warchief, and some NPC in Orgrimmar saying it's Sylvanas and another NPC saying it is Vol'jin). Using level-scaling, allow players to chart their own path over, say, 50 levels throughout the old world and Cata. maybe 20 levels covering Outland, Northrend and MOP (again, using level scaling so you can chart your course and level entirely in Pandaria if you wan), then 15 levels for WoD and Legion?