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)
The Northrend vendor, Auzin, is located at Tirionâs fountain in the center of Dalaran, and he sells these Northrend-themed rewards: the Ironbound Wraithcharger, Will of Northrend, Hourglass of Eternity, Wrath-model badge gear, and the old Wrath justice point reputation commendations.