Hello !
Does the challenge have rewards ? If so could i get the link to the post that list them ?
If not i have some ideas.
Since katana wepon are quite rare, maybe every 5 or 10 lvl we get one with a unique skin by mailbox.
Or add one npc for the challenge in SW / UC that give a quest with a katana reward every 5 or 10 lvl.
Getting some unique looking sword would be the best reward i think because even after lvl 60 we will still want to play melee with them thanks to transmog.
Also some sword that look like katana can't me equiped. Like the lvl 2 "Practice Sword".