I very much doubt that the image that ArenaNet have teased is the Druid so I suspect it's one of the Revenant's new Legends. We only know two at the moment (Jalis Ironhammer and Mallyx the Unyielding) but there was data mined information several months ago that showed the Revenant would receive three additional Legends:

• Glint
• Shiro Tagachi
• Ventari 

For anyone who doesn't know (unsure who!) Ventari was an elder Centaur that lived in Maguuma Jungle. Officially, "he abhorred the violence that engulfed his species and that of the humans, setting up a camp in the arid tops of the Maguuma Jungle." 

Considering the picture, I think it's highly unlikely at this stage to be the Druid. That said, stranger things have happened.

I'll keep you posted.