I don't think anything here says players are getting access to this condition. Sounds more like something that will get used against us, at least for now.
It sounds to me like it will be permanent, at least based on this much information. They said some months ago that they planned to start adding more new skills and traits to the game in this way.
Interesting that they end the trailer with "the Nightmare Grows." That's both, potentially, a Nightmare Court reference and a plant reference, and there were clearly vines growing out of the base of the structure along with glowy purple areas very reminiscent of the Nightmare Court. I may be grasping at nothing here, but maybe it involves the unrevealed jungle dragon?