Boxing & unboxing is the process of converting a primitive value into an object oriented wrapper class (boxing), or converting a value from an object oriented wrapper class back to the primitive value (unboxing).
The Old Dalaran will stay in Northrend, so yes, mages are going to have 2 portals to dalaran (one to Northrend and one to the Broken Isles)
1) Set your Hearthstone to Dalaran. 2) Use the Caverns of Time NPC inside the Violet Citadel to port to Tanaris and southern Kalimdor. 3) Use the Home City portal inside your factions section of Dalaran to get back to your factions capital. - Use the Uldum Portal once unlocked to get to southern Kalimdor. - Use the Twilight Highlands Portal to get to mid Eastern Kingdoms. - Use the Mount Hyjal Portal to get to northern Kalimdor.