The latest dev diary by Turbine walks us through these changes as the team works to clearly define the three styles of play. One of the big changes is the addition of a brand-new gambit builder, which comes from javelin throws when players are fighting in the new ranged (Assailment) stance. This gambit builder will replace the spear thrusts in the stance, as it's somewhat difficult to jab someone from 40 meters away with a stick.
Another significant change is the addition to what Turbine calls "flavoring" for gambits. These are bonus effects that change depending on the Warden's stance to strengthen tanking, melee DPS, or ranged DPS. Other fun tweaks to the class include allowing Wardens to prep a gambit ahead of a battle and a huge overhaul to the three trait lines.