latest tweet got me thinking
Combined with some of the datamining from that_shaman, it is very suggestive we might see an event before Heart of Thorns.
Though of course, it could just be for something else far down the line. Although part of me thinks it will be something to do with the next beta weekend event.
https://www.guildwars2.com/en/news/the-mordrem-are-coming/
Seems this event is for the newer players to practice against mordrem etc. Learn some of the basic mechanics whilst seeing the living story first hand for a weekend.