I thought they specifically said that it wouldn't be a dagger because it doesn't give the art team anything to work with to make it actually look somewhat legendary.
If it ends up being a caster weapon, it'll have to be a staff.
Priests, shamans, and druids can't use swords.
Mages and warlocks can't use maces.
The only class that would be negatively affected by a staff at all would be shaman since they would typically use a 1h + shield, but one out of five isn't bad.