Now that we know the origin of Frostmourne and we're all chummy with the Runecarver, isn't this the ideal opportunity to right the injustice of Legion where DK's were not able to get this as a transmog option?
Similar to other exp's where there has been a couple of class specific quests (Lock green fel fire etc), there is precedent for this to become an opportunity.
Not saying that this has to be an actual weapon, just a transmog 'skin', maybe 'Memory of a shattered blade' or something like that. If I can mog the fabled Ashbringer on my paladin, my DK brothers should be able to mog their equivalent.