Seems rather ridiculous to me. The Perdu weapons seemed like a good means of helping balance out all the jobs who lacked a weapon with decent damage:delay ratio and came with a decent boost to boot; it actually somewhat levelled the playing field, making Bow/Scythe/Sword (I sortof wonder about the club, Perdu Hanger/Club on BLU would be a damn ton of att/acc...but blagh) somewhat less laughable. With something like Perdu Katana they may as well just toss in Perdu Axe, Perdu Cesti and Perdu Dagger and imbalance them all over again.
Well, Cesti, Dagger, and Axe wouldn't exist. Since the Perdu Weapons, even if this Katana is a mirror, were added because of Waghs, Blau, and Maneater. Thats why you're not seeing a Perdu Great Katana, because Onimaru exists. In a sense, it's fair for a Katana version to be around, as Katana didn't have one of these weapons.
Also, it might not be as easily attained as GET RANK, SPEND POINTS. Remember, theres a new battle ground type coming in. It could be hellaciously tough to get. It doesn't have a name yet, after all.