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 only other shortcuts I can think of is to use the portal in Dalaran to get to the Caverns of Time in Tanaris, then travel from there to Un'Goro. You can also be teleported to the Caverns of Time from Shattrath (from World's End Tavern), but you need... honored rep with the Keepers of Time I think. Hope that helps!