Actually the mission on the PTS - [Weekly] The Dread Masters - recommends 156 gear (Basic) for Story Mode and 168 gear (Underworld) for Hard Mode. That tends to suggest that SM drops Arkanian and HM drops Kell Dragon. As a comparison, the currently TFB and S&V weeklies recommend 156 for SM and 162 for HM.
As another poster noted, all the Basic/Elite/Ultimate vendors are gone on the PTS,
Also, not sure if anyone has mentioned this, but to complete the Weekly, you need to either defeat Corruptor Zero in Operation: Dread Fortress or Dread Master Raptus in Operation: Dread Palace.
The problem with HM dropping KD is that a new tier is supposed to be coming out, and since NiM won't be out right away, it has to be in HM or SM, which suggests it will be in HM.