How difficult would it be to implement… a moving boss (on a specific looping path – or not looping, could end up as a challenge to kill is before it reaches its target) that is also a “fortress” style boss? Something like a giant char war machine, or rampant Asura creation that is closing in on destroying a town, and players have to climb up it, destroying power nodes along the way, while it fights back mostly with knockbacks and AoEs that are difficult to dodge because of limited standing space, and can knock the player off the boss.
I don’t know how well the GW2 physics system could deal with that…