I think having 2 cities with the same name in the game would lead to problems, if Blizz say Dalaran is moving then the best option is to remove it from Cristal song once and for all.
Move it to the caverns of time, problem solved... Afterhall, VH is in the past.
EDIT: Still i must admit, seeing Dalaran going away its a weird sensation, its my favorite city, and not seeing it in Northrend is strange.
Another option is keep it as a neutral sanctuary city, i know jaina taked it, but Garrosh has been slain and Vol'Jin is now the Horde's big boss, it does not need to become aliance only.